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8.08 Product rule

Worksheet
Product rule
1

To differentiate y = x^{6} \left(x^{4} + 4\right) using the product rule, let u = x^{6} and v = x^{4} + 4, then:

a

Find u'.

b

Find v'.

c

Hence, find \dfrac{dy}{dx}.

2

To differentiate y = \left(x^{7} + 5\right) \left(x^{6} + 6\right) using the product rule, let u = x^{7} + 5 and v = x^{6} + 6, then:

a

Find \dfrac{d u}{d x}.

b

Find \dfrac{d v}{d x}.

c

Hence, find \dfrac{dy}{dx}.

3

Consider the function y = x^{3} \left(x^{2} + 9\right).

a

Differentiate y by first expanding the brackets.

b

Differentiate y using the product rule, letting u = x^{3} and v = x^{2} + 9.

4

Differentiate the following functions:

a

f \left( x \right) = \left( 3 x - 2\right) \left( 4 x - 5\right)

b

g \left( t \right) = \left( 2 t^{3} - 3\right) \left(3 - t\right)

c

g \left( y \right) = \left( 7 y^{4} - y^{2}\right) \left(y^{2} - 5\right)

d

f \left( x \right) = \left(x^{\frac{4}{3}} + 6 \sqrt{x}\right) \left( 6 x + 3\right)

e

f \left( x \right) = x \sqrt{3 - x}

f

f \left( x \right) = \sqrt[3]{x^{2}} \left( 2 x - x^{2}\right)

g

f \left( x \right) = x^{\frac{1}{3}} \left(1 - x\right)^{\frac{2}{3}}

h

y = \left(2 + \sqrt{x}\right) \left(6 - x^{2}\right)

i

y = \left(1 + \dfrac{1}{x}\right) \left(3 + x - x^{2}\right)

j

y = x^{3} \left( 5 x + 3\right)^{7}

k

y = 6 x^{5} \left(x^{2} + 3\right)^{3}

l

y = 3 x \left(x^{2} + x + 1\right)^{9}

m

y = \left( 8 x - 9\right)^{5} \left( 5 x + 7\right)^{7}

n

y = \left( 3 x + 2\right) \sqrt{5 + 4 x}

o

y = 8 x \left(5 + 8 x\right)^{\frac{7}{4}} - 3

p

y = 8 x^{5} \sqrt{ 8 x + 3}

q

y = 6 x \sqrt{x + 1}

r

y = - 4 x \sqrt{1 - 2 x}

5

Consider the function y = \left( 4 x - 3\right) \left( 5 x - 2\right).

a

Differentiate y.

b

Hence, differentiate f \left( x \right) = x^{3} \left( 4 x - 3\right) \left( 5 x - 2\right).

6

For each of the following functions:

i

Identify possible factors u and v for the function.

ii

Differentiate the function. Give your answer in factorised form.

iii

State the values of x for which the derivative is zero.

a
y = x \left(x - 8\right)^{4}
b
y = x^{3} \left(x + 3\right)^{4}
c
y = \left(x + 2\right) \left(x + 5\right)^{6}
7

The derivative of f \left( x \right) = \left( 3 x^{n} + 4\right) \left( 5 x^{2} - 2 x\right) is of degree 5. Find the value of n.

Gradients, tangents and normals
8

Consider the function f \left( x \right) = \left(x^{2} - 3 x\right) \left( 2 x - 5\right).

a

Find f \left( 3 \right).

b

Find f' \left( 0 \right).

c

Find f' \left( - 3 \right).

9

Consider the function g \left( x \right) = x^{3} f \left( x \right), where f \left( x \right) is a function of x. Given that f \left( 3 \right) = 1 and f' \left( 3 \right) = - 3, find g' \left( 3 \right).

10

Consider the function f \left( x \right) = \left(x + 1\right) \left(x + 3\right)^{3}.

a

Find f' \left( x \right) in factorised form.

b

Find the equation of the tangent at \left( - 1 , 0\right).

c

Find the equation of the normal at \left( - 1 , 0\right).

11

Find the values of x such that the gradient of the tangent to the curve y = 2 x \left(x + 3\right)^{2} is equal to 14.

12

Find the gradient of the tangent to the curve y = x \sqrt{ 2 x + 5} at the point where x = 2.

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Outcomes

MA11-1

uses algebraic and graphical techniques to solve, and where appropriate, compare alternative solutions to problems

MA11-5

interprets the meaning of the derivative, determines the derivative of functions and applies these to solve simple practical problems

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