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BAC1 ss · Mathematics
Derivatives · Derivatives

Differentiation rules

Few real-life functions are a bare polynomial: a profit that depends on time multiplied by a factor, a number of users that grows like a quotient, a sum of money that grows exponentially. To differentiate these combinations without going back to limits every time, there are fixed rules: product, quotient, chain and exponential. Applied in the right order, they differentiate any function you will meet in 1st Bachillerato.

Before you start, make sure you know: The concept of the derivative (4th ESO)
Before you start, make sure you know: Operations with polynomials (4th ESO)

The product rule

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Apply the product rule to find the derivative of the following functions (do not expand the brackets before differentiating): a) $f(x) = (x^2 + 3) \cdot (5x - 1)$ b)…

Apply the product rule to find the derivative of the following functions (do not expand the brackets before differentiating):

  1. a) $f(x) = (x^2 + 3) \cdot (5x - 1)$
  1. b) $g(x) = (x + 2) \cdot (x^3 - 4x)$
Solve

The quotient rule

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Calculate the derivative of these rational functions using the quotient rule: a) $f(x) = \frac{3x - 5}{x + 2}$ b) $g(x) = \frac{x^2}{2x + 1}$ c)…

Calculate the derivative of these rational functions using the quotient rule:

  1. a) $f(x) = \frac{3x - 5}{x + 2}$
  1. b) $g(x) = \frac{x^2}{2x + 1}$
  1. c) $h(x) = \frac{10}{x^2 + 4}$
Solve
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A sociological study indicates that the number of users of a new social network (in millions) is given by the function $U(t) = \frac{40t}{t^2 + 4}$, where $t$ is the…

A sociological study indicates that the number of users of a new social network (in millions) is given by the function $U(t) = \frac{40t}{t^2 + 4}$, where $t$ is the time in months since its launch. Apply the quotient rule to find the derivative function $U'(t)$ and determine in which month user growth stops and begins to decrease. What is the rate of user loss after one year ($t=12$)?

Solve

The chain rule

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Apply the chain rule to calculate the derivative function of these composite functions: a) $f(x) = (3x^2 - 5)^4$ b) $g(x) = \sqrt{x^2 + 1}$ c) $h(x) = (1 - x)^5$

Apply the chain rule to calculate the derivative function of these composite functions:

  1. a) $f(x) = (3x^2 - 5)^4$
  1. b) $g(x) = \sqrt{x^2 + 1}$
  1. c) $h(x) = (1 - x)^5$
Solve
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Calculate the equation of the tangent line to the curve $f(x) = \sqrt{x^2 + 5}$ at the point where said curve intersects the line $y = 3$ (consider only the solution in…

Calculate the equation of the tangent line to the curve $f(x) = \sqrt{x^2 + 5}$ at the point where said curve intersects the line $y = 3$ (consider only the solution in the first quadrant). Once the line is found, determine the area of the triangle formed by this tangent line with the coordinate axes.

Solve

Derivative of the exponential function

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The number of views of a viral video (in thousands) is given by the function $V(t) = 2 \cdot e^{0,5t}$, where $t$ is the time in days. Knowing that the derivative of…

The number of views of a viral video (in thousands) is given by the function $V(t) = 2 \cdot e^{0,5t}$, where $t$ is the time in days. Knowing that the derivative of $e^{u}$ is $u' \cdot e^u$, calculate the rate of growth of the views on the second day ($t = 2$).

Solve

Combining the rules

Most real functions mix the chain rule with the product or the quotient rule. The strategy is always the same: first identify the "outermost" operation (a product? a quotient? a single composite function?) and apply its rule; within each derivative that appears, check again whether the chain rule is needed.

Practice★★☆Not started
Calculate the derivative of the following function containing a square root, simplifying the final result: $f(x) = \sqrt{x^2 + e^x}$ Use the chain rule for functions of…

Calculate the derivative of the following function containing a square root, simplifying the final result:

$f(x) = \sqrt{x^2 + e^x}$

Use the chain rule for functions of the form $\sqrt{u}$.


Solve
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Obtain the derivative function of the following function using the product rule and the derivative of the exponential function: $f(x) = (x^2 + 3x - 1) \cdot e^{2x}$…

Obtain the derivative function of the following function using the product rule and the derivative of the exponential function:

$f(x) = (x^2 + 3x - 1) \cdot e^{2x}$

Factorise the expression for $f'(x)$ by taking out the exponential term as a common factor.

Solve

Summary

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