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9.08 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}
5

Consider the function f \left( t \right) = \dfrac{\left( 4 t^{2} + 3\right)^{3}}{\left(5 + 2 t\right)^{5}}. Find f' \left( t \right).

Gradients and tangents
6

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.

7

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).

8

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.

9

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

10

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

11

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

12

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

13

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

14

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

Increasing and decreasing functions
15

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?

16

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.

17

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?

18

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?

19

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?

20

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 in the intervals \left(-\infty, - 3 \right),\left( - 3 , 3\right) and \left(3, \infty\right)?

c

Find f' \left( 4 \right).

21

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
22

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

23

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

24

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).

25

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

2.5.1.1

understand and apply the product rule and quotient rule for power and polynomial functions

2.5.1.3

select and apply the product rule, quotient rule and chain rule to differentiate power and polynomial functions; express derivative in simplest and factorised form

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