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BAC1 ss · Mathematics
Numbers · Real numbers

Powers with integer exponents

The interest on a deposit, the growth of a population and the capacity of a hard drive have something in common: they grow (or shrink) by multiplying by the same factor again and again. That repetition is exactly what a power describes, and mastering its properties lets you calculate in one step what, factor by factor, would take minutes.

Before you start, make sure you know: Prime factorisation (2nd ESO)
Before you start, make sure you know: Properties of powers (4th ESO)

Powers with integer exponents: definition and sign

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It is very common to confuse the effect of brackets when the base is negative. Calculate the following values and explain the difference between them: a) $(-2)^4$ b)…

It is very common to confuse the effect of brackets when the base is negative. Calculate the following values and explain the difference between them:

  1. a) $(-2)^4$
  1. b) $-2^4$
  1. c) $(-2)^3$
  1. d) $-2^3$
Solve
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Calculate the value of the following combined expressions, respecting the order of operations and the laws of indices: a) $2^3 + 2^2 + 2^1 + 2^0$ b)…

Calculate the value of the following combined expressions, respecting the order of operations and the laws of indices:

  1. a) $2^3 + 2^2 + 2^1 + 2^0$
  1. b) $10^3 \cdot 10^{-2} + 5 \cdot 10^0$
  1. c) $(3-1)^2 \cdot 3^{-1}$
Solve

Rules for operating with powers

Illustrated formulas for the properties of powers: adding exponents for the product of powers with the same base and multiplying exponents for a power of a power. am · an = am+n same base: add the exponents (am)n = amn power of a power: multiply
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Apply the laws of indices to simplify the following expression and leave the result as a single power with a positive base: $$\frac{3^5 \cdot 3^2}{3^4}$$

Apply the laws of indices to simplify the following expression and leave the result as a single power with a positive base:

$$\frac{3^5 \cdot 3^2}{3^4}$$
Solve
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Simplify the following expression using the power of a power and product of powers laws. Express the result as a single power: $$(2^3)^2 \cdot (2^{-2})^4$$

Simplify the following expression using the power of a power and product of powers laws. Express the result as a single power:

$$(2^3)^2 \cdot (2^{-2})^4$$
Solve

Negative exponents: growth and decay

Representation of the negative exponent as the reciprocal of a power, showing that a^(-n) equals 1 divided by a^n. a−n = 1/an negative exponent: invert the base 1,02t (t>0, grows) 1,02−t (decays)
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Calculate the numerical value of the following powers with negative exponents, expressing the final result as an irreducible fraction: a) $5^{-2}$ b)…

Calculate the numerical value of the following powers with negative exponents, expressing the final result as an irreducible fraction:

  1. a) $5^{-2}$
  1. b) $\left(\frac{2}{3}\right)^{-3}$
  1. c) $(-4)^{-2}$
Solve
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Work out and simplify the following expression, leaving the result as an irreducible fraction without negative exponents: $$\frac{\left( \frac{2}{3} \right)^{-2} \cdot…

Work out and simplify the following expression, leaving the result as an irreducible fraction without negative exponents:

$$\frac{\left( \frac{2}{3} \right)^{-2} \cdot \left( \frac{4}{9} \right)^{3}}{\left( \frac{3}{2} \right)^{4} \cdot 2^{-1}}$$
Solve

Simplifying by prime factorisation

Prime factorisation of the numbers 12 and 18 into powers of the prime bases 2 and 3 so that their exponents can be worked with. 12 = 2² · 3 18 = 2 · 3² same base: 2 and 3 exponents can now be added
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To calculate the storage capacity of a new cloud server, an engineer needs to simplify the following numerical expression. Use the laws of indices to reduce it to a…

To calculate the storage capacity of a new cloud server, an engineer needs to simplify the following numerical expression. Use the laws of indices to reduce it to a single power with a prime base or a product of powers with positive exponents:

$$\frac{12^4 \cdot 18^{-2} \cdot 2^5}{32 \cdot 3^{-3}}$$
Solve
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Calculate the value of the following numerical expression by expressing the bases in prime factors and simplifying as much as possible. The result must be an integer or…

Calculate the value of the following numerical expression by expressing the bases in prime factors and simplifying as much as possible. The result must be an integer or an irreducible fraction:

$$\frac{15^6 \cdot 12^{-4} \cdot 80^3}{20^4 \cdot 27^2 \cdot 3^{-5}}$$
Solve

Applications: growth and comparing rates

Cumulative growth diagram illustrating repeated multiplication by a constant factor over time by means of a power. ×3 every hour t=0 t=n

Repeatedly multiplying by the same factor — a population that triples every hour, a capital that appreciates every month — is exactly a power: the base is the factor for each step, and the exponent is the number of steps.

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A biologist observes a population of bacteria that triples every hour. If initially there were $3^2$ bacteria, express using a power of base $3$: a) How many bacteria…

A biologist observes a population of bacteria that triples every hour. If initially there were $3^2$ bacteria, express using a power of base $3$:

  1. a) How many bacteria will there be after $5$ hours?
  2. b) How many bacteria will there be after $n$ hours?
Initial population 3² bacteria t=0 t=1 t=2 t=5 t=n hours 3² 3³ 3⁴ 3²·3⁵ a) 3²·3ⁿ b) ×3 ×3 ... ...
Solve
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In a biotechnology laboratory, a bacterial population triples every hour. If initially there were $3^4$ bacteria, the expression representing the number of bacteria…

In a biotechnology laboratory, a bacterial population triples every hour. If initially there were $3^4$ bacteria, the expression representing the number of bacteria after $t$ hours is $3^4 \cdot 3^t$.

  1. a) How many bacteria will there be after one day ($t=24$)? Express the result as a power.
  1. b) If due to an antibiotic the population decreases by dividing by $9^5$, simplify the resulting expression:
$$\frac{3^4 \cdot 3^{24}}{9^5}$$ Time (t hours) Population 3⁴ 0 3⁴·3¹ 1 3⁴·3²⁴ 24 ÷ 9⁵ antibiotic action (3⁴·3²⁴)/9⁵ ?
Solve
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An investor analyses two financial products. In the first, their capital is multiplied by $1,02$ every month (compound interest). In the second, due to high volatility,…

An investor analyses two financial products. In the first, their capital is multiplied by $1,02$ every month (compound interest). In the second, due to high volatility, the capital is multiplied by $1,05$ one month, but decreases by being multiplied by $0,98$ the following month, repeating this two-month cycle indefinitely.

If the investor deposits an amount $C$ for $2$ years ($24$ months), express using powers with integer exponents the final capital obtained in each option. Which of the two options is more profitable after those $24$ months? Justify your answer by comparing the bases of the resulting powers, once they are written with the same exponent.

Solve

Summary

See all the exercises in this section