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Precalculus · Mathematics
Real Numbers · Real Numbers

"Basic Operations: Fractions, Exponents, and Special Products"

Before you start, make sure you know: Operations with rational numbers (Math 7)
Before you start, make sure you know: Operations with powers (Math 8 (Pre-Algebra))

Emma and Malik both evaluate $4 + 3\cdot 2^2$. Emma gets $16$ and Malik gets $28$. Only one of them can be right, and the difference comes down to the order in which they did the steps. In Precalculus, fractions, exponents, and special products are no longer the topic. They are the tools you use constantly, so they need to be automatic.

Order of operations

When an expression has several operations, everyone must follow the same order, or the same expression would have different values for different people.

Four steps of the order of operations applied to an expression with parentheses, exponents, multiplication, division, addition and subtraction. 12 − 3(2 − 5)² ÷ 9 + (−1)³ 1parentheses 2exponents 3× and ÷, left to right 4+ and −, left to right
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Work out the following combined operation with integers, strictly respecting the order of operations: $5 - 2 \cdot (4 - (-3)^2) + (-2)^3$.

Work out the following combined operation with integers, strictly respecting the order of operations: $5 - 2 \cdot (4 - (-3)^2) + (-2)^3$.

Solve

Operations with fractions

Fractions follow the same order of operations. The only new work is knowing how to combine them.

A fraction bar is a grouping symbol. In a complex fraction (a fraction that contains fractions), treat the numerator and the denominator as if each were in parentheses, simplify each one, and then divide.

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Calculate and fully simplify the result of the following expression with fractions: $\frac{3}{4} - \frac{1}{2} \cdot \left( \frac{5}{6} + \frac{1}{3} \right)$.

Calculate and fully simplify the result of the following expression with fractions: $\frac{3}{4} - \frac{1}{2} \cdot \left( \frac{5}{6} + \frac{1}{3} \right)$.

Solve
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Solve the following operation with nested fractions (complex fractions), simplifying step by step from the inside out:…

Solve the following operation with nested fractions (complex fractions), simplifying step by step from the inside out: $\frac{1 - \frac{1}{1 - \frac{1}{2}}}{1 + \frac{1}{1 + \frac{1}{2}}}$.

Solve

Fractions of a whole and of a remainder

Word problems with fractions all hinge on one word. "Of" means multiply. Another important detail is what the fraction refers to: the whole, or what is left. A good habit is to write every amount as a fraction of the original whole.

The next example works backward from a known amount to the total.

A bar split into eight equal parts: two eighths for T-shirts, three eighths for the banner, and three eighths left, worth 300 dollars. T-shirts2/8 banner3/8 left3/8 = $300
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An agricultural irrigation water tank is full to $\frac{3}{5}$ of its capacity. If the equivalent of $\frac{1}{4}$ of the tank's total capacity is extracted to water a…

An agricultural irrigation water tank is full to $\frac{3}{5}$ of its capacity. If the equivalent of $\frac{1}{4}$ of the tank's total capacity is extracted to water a plot, determine what fraction of the tank's total capacity still contains water.

Solve
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A technology company allocates $\frac{2}{5}$ of its annual budget to staff salaries and $\frac{1}{3}$ of the remaining budget to marketing campaigns. If after these two…

A technology company allocates $\frac{2}{5}$ of its annual budget to staff salaries and $\frac{1}{3}$ of the remaining budget to marketing campaigns. If after these two allocations it still has $54000$ dollars left for other operating expenses, set up the necessary operations with fractions to determine the total budget of the company.

Solve

Properties of integer exponents

A power $a^n$ with $n$ a positive integer means $n$ factors of $a$. To extend it to zero and negative exponents, look for a pattern. Each step down in the exponent divides by $2$:

$$2^3 = 8,\quad 2^2 = 4,\quad 2^1 = 2,\quad 2^0 = 1,\quad 2^{-1} = \tfrac12,\quad 2^{-2} = \tfrac14,\quad 2^{-3} = \tfrac18.$$
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Express the result as a single power using the properties of multiplication and division of powers with the same base: $\frac{7^5 \cdot 7^{-3}}{7^4}$.

Express the result as a single power using the properties of multiplication and division of powers with the same base: $\frac{7^5 \cdot 7^{-3}}{7^4}$.

Solve
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Calculate the exact value of the following numerical expression, applying the definition of a negative exponent:…

Calculate the exact value of the following numerical expression, applying the definition of a negative exponent: $\left( \frac{2}{3} \right)^{-2} + \left( \frac{1}{4} \right)^{-1}$.

Solve
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Simplify the following algebraic expression by applying the properties of powers and express the final result using only positive exponents: $(x^3 \cdot x^{-5})^2$.

Simplify the following algebraic expression by applying the properties of powers and express the final result using only positive exponents: $(x^3 \cdot x^{-5})^2$.

Solve

Negative exponents with fractions and variables

Most exponent problems in Precalculus have coefficients, several variables, and parentheses all at once. Use the same routine every time:

  1. Distribute the outer exponent to every factor inside, including the numerical coefficient.

  2. Combine powers with the same base.

  3. Move factors with negative exponents across the fraction bar. The exponent changes sign when it crosses.

A factor with a negative exponent moves across the fraction bar and its exponent becomes positive. x⁻³ / y⁻² = y² / x³ A factor crosses the fraction bar, and its exponent changes sign. Only the factor with the exponent moves.

For a big expression in brackets with an outer negative exponent, simplify the inside completely first (or apply the outer exponent last). Write the name of the rule you use on each line, for example "power of a product" or "quotient of powers", so you can state your order of properties.

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Calculate and fully simplify the following expression, paying special attention to negative exponents and the order of operations:…

Calculate and fully simplify the following expression, paying special attention to negative exponents and the order of operations: $\left( \frac{3}{2} - \frac{1}{4} \right)^{-2} \cdot \left( \frac{5}{3} \right)^{-1}$.

Solve
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Simplify the following algebraic expression, grouping equal bases and leaving the final result expressed exclusively with positive exponents:…

Simplify the following algebraic expression, grouping equal bases and leaving the final result expressed exclusively with positive exponents: $\frac{(2a^{-2} b^3)^{-3}}{4a^4 b^{-5}}$.

Solve
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Fully simplify the following complex algebraic expression, indicating the order of the properties of powers used and leaving the final result without negative exponents:…

Fully simplify the following complex algebraic expression, indicating the order of the properties of powers used and leaving the final result without negative exponents: $\left[ \frac{(x^2 y^{-1})^{-2} \cdot (x^{-3} y^2)^3}{(x y)^{-4}} \right]^{-1}$.

Solve

Prime factorization and powers

The exponent rules need the same base. When the bases are different numbers, factor them into primes. Then everything lives on a few common bases and the rules apply.

Factor tree of 36 showing 36 equals 2 squared times 3 squared. 36 6 6 2 3 2 3 36 = 2² · 3²

Exponential equations

If $b^x = b^y$ with $b > 0$ and $b \ne 1$, then $x = y$, because equal powers of the same base must have equal exponents. So write both sides with the same base and set the exponents equal.

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Simplify the following numerical fraction by first factorizing its terms into powers of prime numbers: $\frac{2^4 \cdot 3^2 \cdot 5}{2^2 \cdot 3^3 \cdot 5^2}$.

Simplify the following numerical fraction by first factorizing its terms into powers of prime numbers: $\frac{2^4 \cdot 3^2 \cdot 5}{2^2 \cdot 3^3 \cdot 5^2}$.

Solve
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Simplify the following numerical expression by first factorizing the composite bases into prime numbers and applying the properties of powers:…

Simplify the following numerical expression by first factorizing the composite bases into prime numbers and applying the properties of powers: $\frac{18^4 \cdot 12^{-3}}{24^2 \cdot 9^{-2}}$.

Solve
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Determine the value of the integer $n$ so that the following exponential equality is true, transforming all composite bases into powers of base $2$:…

Determine the value of the integer $n$ so that the following exponential equality is true, transforming all composite bases into powers of base $2$: $\frac{4^n \cdot 8^3 \cdot 2^{-5}}{16^2} = 2^{10}$.

Solve

Putting exponents and fractions together

Real problems blend everything so far. Halving, doubling, and "fraction of what is left" all produce powers and fractions. Powers of $2$ also show up in computing: file sizes in bytes are powers of $2$.

Bars that shrink by half each time, labeled with the powers of 2 from 2 to the 0 down to 2 to the minus 3. 2⁰1 2⁻¹1/2 2⁻²1/4 2⁻³1/8 halving k times multiplies by (1/2)^k = 2⁻ᵏ

For "fraction of the remaining" problems, as in the fundraiser example, write every part as a fraction of the total first. Turn any power such as $\left(\tfrac32\right)^{-1}$ into a plain fraction before you multiply.

For a long numerical expression, simplify the numerator and the denominator on their own and divide at the end.

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In a physical optics experiment, the intensity of a laser signal is halved each time it passes through an attenuating filter. If the original signal has an intensity…

In a physical optics experiment, the intensity of a laser signal is halved each time it passes through an attenuating filter. If the original signal has an intensity $I_0$ and passes through $5$ consecutive filters, and is subsequently amplified by multiplying by a factor of $\left( \frac{1}{4} \right)^{-2}$, express the final intensity of the signal in terms of $I_0$ using a single power with base $2$.

Solve
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The total storage capacity of a data server is structured as follows: $\frac{1}{8}$ of the total capacity is reserved for the operating system; of the remaining…

The total storage capacity of a data server is structured as follows: $\frac{1}{8}$ of the total capacity is reserved for the operating system; of the remaining capacity, a fraction equivalent to $\left( \frac{3}{2} \right)^{-1}$ is allocated to databases, and the leftover space is used for backups. If the backups occupy exactly $3 \cdot 2^{40}$ bytes, set up and solve the necessary operations to determine the total capacity of the server, expressing the result as a power of base $2$.

Solve
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Calculate the exact value of the following numerical expression, detailing each logical step and using a combination of the properties of fractions, negative exponents…

Calculate the exact value of the following numerical expression, detailing each logical step and using a combination of the properties of fractions, negative exponents and algebraic identities: $\frac{\left( 1 - \frac{3}{5} \right)^{-2} + \left( \frac{5}{2} - 1 \right)^2}{\left( \frac{2}{3} \right)^{-3} \cdot \left( \frac{1}{2} \right)^2}$.

Solve

Special products

Some products show up so often that you should recognize them on sight. They come from multiplying out $(a+b)(a+b)$ and $(a+b)(a-b)$ term by term.

Think of $(a+b)^2$ as the area of a square with side $a+b$. It splits into one $a\times a$ square, one $b\times b$ square, and two $a\times b$ rectangles. The two rectangles are the "$2ab$".

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Expand the following algebraic expressions using the corresponding algebraic identities: a) $(3x + 5)^2$ b) $(2x - 1)(2x + 1)$

Expand the following algebraic expressions using the corresponding algebraic identities:

  1. a) $(3x + 5)^2$
  2. b) $(2x - 1)(2x + 1)$
Solve

Using special products in problems and proofs

Special products are useful in three ways. You can expand a geometric formula, you can recognize a perfect square "backward", and you can prove identities.

Area problems

If a square of side $s$ grows by $k$ on each side, the new area is $(s+k)^2 = s^2 + 2sk + k^2$. The gain is $2sk + k^2$.

A square of side s enlarged by k on each side, split into s squared, two rectangles s times k, and k squared. s² sk sk k² s k s k (s + k)² = s² + 2sk + k²

Recognizing a perfect square

An expression $A^2 \pm 2AB + B^2$ factors back into $(A \pm B)^2$. To test a trinomial, check three things: the first and last terms are perfect squares, and the middle term is twice the product of their roots.

Proving an identity

To prove an identity, start from one side, expand or simplify one step at a time, and reach the other side. Do not substitute numbers: examples can test a claim, but they never prove it.

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The side of a square plot intended for the installation of solar panels measures $3x - 2$ feet. If it is decided to expand the land by increasing each side by $4$ feet,…

The side of a square plot intended for the installation of solar panels measures $3x - 2$ feet. If it is decided to expand the land by increasing each side by $4$ feet, express the area of the new land and determine the difference in area between the new and old plots, using the expansion of algebraic identities.

Solve
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In the design of a precision mechanical part, it is specified that the area of a rectangular cross-section must correspond to the formula $A = 16x^2 - 24x + 9$ square…

In the design of a precision mechanical part, it is specified that the area of a rectangular cross-section must correspond to the formula $A = 16x^2 - 24x + 9$ square inches. Prove algebraically that this area always corresponds to a perfect square for any real value of $x$, and determine the expression that defines the side length of this square.

Solve
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Prove rigorously, by algebraic manipulation, that the difference between the square of the sum of any two real numbers and the square of their difference is always equal…

Prove rigorously, by algebraic manipulation, that the difference between the square of the sum of any two real numbers and the square of their difference is always equal to four times the product of these numbers. That is, prove that $(a+b)^2 - (a-b)^2 = 4ab$.

Solve

Algebraic fractions

An algebraic fraction (a rational expression) has polynomials in the numerator and denominator. It is simplified the same way as a numerical fraction: factor, then cancel common factors. Special products give you the factoring.

Left: cancelling a common factor is allowed. Right: cancelling separate terms is not allowed. Allowed: common factor (x − 2)(x + 2) (x + 2)(x + 2) = (x − 2) / (x + 2) Not allowed: separate terms x² + 4 x + 2 nothing multiplies the whole top

To add or subtract algebraic fractions, factor each denominator and build the least common denominator (LCD) from the factors. Some problems call this the lowest common multiple of the denominators. Then rewrite each fraction over the LCD.

Testing a "simplification"

To show that a claim is false, one counterexample is enough. To find when it is true, expand and solve.

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Given the algebraic expression $P(x,y) = \frac{x^2 - y^2}{(x-y)^2}$, evaluate its exact value for $x = \frac{1}{2}$ and $y = -\frac{1}{3}$. Simplify the expression…

Given the algebraic expression $P(x,y) = \frac{x^2 - y^2}{(x-y)^2}$, evaluate its exact value for $x = \frac{1}{2}$ and $y = -\frac{1}{3}$. Simplify the expression theoretically before substituting the values to facilitate the numerical calculation.

Solve
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Subtract the following algebraic fractions and simplify the result to obtain a single irreducible fraction. Apply factorization using algebraic identities in the…

Subtract the following algebraic fractions and simplify the result to obtain a single irreducible fraction. Apply factorization using algebraic identities in the denominators to find the lowest common multiple: $\frac{x^2 - 1}{x^2 + 2x + 1} - \frac{x - 1}{x + 1}$.

Solve
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During the resolution of a kinematics problem, a student has made the following algebraic simplification: $\frac{x^2 + y^2}{x+y} = x+y$. Explain using an explicit…

During the resolution of a kinematics problem, a student has made the following algebraic simplification: $\frac{x^2 + y^2}{x+y} = x+y$.

Explain using an explicit numerical counterexample why this operation is incorrect. Next, expand the expression $(x+y)^2$ to algebraically justify the error made, and state under what unique and exceptional condition on the variables $x$ and $y$ the student's statement would be numerically true.

Solve

Back to the start: $4 + 3\cdot 2^2$. The exponent comes first, $2^2 = 4$. Then multiplication, $3\cdot 4 = 12$. Last comes addition, $4 + 12 = 16$. Emma was right. Malik added $4 + 3$ before multiplying, which is not allowed.

Summary

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