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VCE 12 Methods 2023

5.04 The quotient rule

Worksheet
Quotient rule
1

Consider the function y = \dfrac{3}{x}.

a

By first rewriting it in negative index form, differentiate y.

b

By using the substitutions u = 3 and v = x, differentiate y using the quotient rule.

c

Find the value of x for which the gradient is undefined.

2

Consider the function y = \dfrac{2 x - 5}{5 x - 2}.

a

Using the substitution u = 2 x - 5, find u'.

b

Using the substitution v = 5 x - 2, find v'.

c

Hence find y'.

d

Is it possible for the derivative of this function to be zero?

3

Consider the function y = \dfrac{5 x^{2}}{2 x + 8}.

a

Using the substitution u = 5 x^{2}, find u'.

b

Using the substitution v = 2 x + 8, find v'.

c

Hence find y'.

4

Differentiate the following functions using the quotient rule:

a
f(x)=\dfrac{7x}{8x-1}
b
y=\dfrac{4x^2}{3x-7}
c
y = \dfrac{3 x}{5 x - 4}
d
y = \dfrac{3 x^{2} + 2}{5 x^{2} + 4}
e
f(x)=\dfrac{2x+1}{x^2 -6x}
f
y=\dfrac{(x-5)^3}{8x}
g
f(x)=\dfrac{\sqrt{x-10}}{4x^2-6}
h
y=\dfrac{(2x-3)^4}{\sqrt{2x+5}}
i
y = \sqrt{\dfrac{2 + 7 x}{2 - 7 x}}
j
f \left( t \right) = \dfrac{\left( 4 t^{2} + 3\right)^{3}}{\left(5 + 2 t\right)^{5}}
k
y = \dfrac{x^{2} + 3 x - 2}{x + 2}
Gradients and tangents
5

Consider the function y = \dfrac{6}{\sqrt{x}} - 5.

a

Find the gradient function using the quotient rule.

b

Find the gradient of the function at x = 25.

6

Find the gradient of the tangent to the curve y = \dfrac{9 x}{4 x + 1} at the point \left(1, \dfrac{9}{5}\right).

7

Find the values of x such that the gradient of the tangent to the curve y = \dfrac{6 x - 1}{3 x - 1} is - 3.

8

Find the equation of the tangent to y = \dfrac{x}{x + 4} at the point \left(8, \dfrac{2}{3}\right).

9

Find the equation of the tangent to y = \dfrac{x^{2} - 1}{x + 3} at the point where x = 4.

10

Find the value of f' \left( 0 \right) for f \left( x \right) = \dfrac{x}{\sqrt{16 - x^{2}}}.

11

Find the value of f' \left( 4 \right) for f \left( x \right) = \dfrac{4 x^{7}}{\left(x + 4\right)^{4}}.

12

Find f' \left( 1 \right) for f \left( x \right) = \dfrac{6}{3 + 3 x^{2}} using a graphing calculator or otherwise.

13

Find the value of f' \left( 3 \right) for f \left( x \right) = \dfrac{5 x}{9 + x^{2}} using a graphing calculator or otherwise.

Increasing and decreasing functions
14

Consider the function y = \dfrac{1}{9 + x^{2}}.

a

Differentiate y using the quotient rule.

b

For what values of x is the function decreasing?

15

Consider the function y = \dfrac{3 - 4 x}{3 x - 4}.

a

Differentiate y.

b

Is it possible for the derivative to be zero?

c

Solve for the value of x that will make the derivative undefined.

16

Consider the function y = \dfrac{x + 6}{x - 6}.

a

Differentiate y.

b

Is it possible for the derivative to be zero?

c

Solve for the value of x that will make the derivative undefined.

d

Is the function increasing or decreasing near this value of x?

17

Consider the function y = \dfrac{5 x}{3 x - 4}.

a

Differentiate y.

b

Is it possible for the derivative to be zero?

c

Solve for the value of x that will make the derivative undefined.

d

Is the function increasing or decreasing near this value of x?

18

Consider the function y = \dfrac{2 x + 3}{2 x - 3}.

a

Differentiate y.

b

Is it possible for the derivative to be zero?

c

Solve for the value of x that will make the derivative undefined.

d

Is the function increasing or decreasing near this value of x?

19

Consider the function f \left( n \right) = \dfrac{1}{n + 3} + \dfrac{1}{n - 3}.

a

Differentiate f \left( n \right).

b

Is the function increasing or decreasing over its domain?

c

Find f' \left( 4 \right).

20

Consider the function f \left( x \right) = \dfrac{1}{4 + \sqrt{x}} + \dfrac{1}{4 - \sqrt{x}}.

a

Find the gradient function.

b

Is the function increasing or decreasing over its domain?

Applications
21

Differentiate y = \dfrac{x^{2}}{x + 3} and find the value of a if y' = 0 at x = a.

22

Differentiate y = \dfrac{x^{2} + k}{x^{2} - k} and find the possible values of k given that y' = 1 at x = - 3.

23

Consider the function g \left( x \right) defined as g \left( x \right) = \dfrac{f \left( x \right)}{x^{3} + 3}, where f \left( x \right) is a function of x.

Given that f \left( 2 \right) = 2 and f' \left( 2 \right) = 6, determine the value of g' \left( 2 \right).

24

Consider the identity 1 + x + x^{2} + \text{. . .} + x^{n - 1} = \dfrac{x^{n} - 1}{x - 1}, where x \neq 1 and n is a positive integer.

a

Form an expression for the sum 1 + 2 x + 3 x^{2} + \text{. . .} + \left(n - 1\right) x^{n - 2}.

b

Hence, find the value of 1 + 2 \times 5 + 3 \times 5^{2} + \text{. . .} + 8 \times 5^{7}.

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Outcomes

U34.AoS3.3

derivatives of f(x) +/- g(x), f(x) x g(x), f(x)/g(x) and (𝑓 ∘ 𝑔)(𝑥) where f and g are polynomial functions, exponential, circular, logarithmic or power functions and transformations or simple combinations of these functions

U34.AoS3.12

the sum, difference, chain, product and quotient rules for differentiation

U34.AoS3.17

apply the product, chain and quotient rules for differentiation to simple combinations of functions by hand

U34.AoS3.16

find derivatives of polynomial functions and power functions, functions of the form f(ax+b) where f is x^n, sine, cosine; tangent, e^x, or log x base e and simple linear combinations of these, using pattern recognition, or by hand

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