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9.07 The 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

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.

3

Consider the function y = \left(x + 5\right) \left(x + 9\right).

a

Differentiate y by first expanding the brackets.

b

Differentiate y by using the product rule.

c

Find the gradient at x = 3.

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).

Applications
6

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).

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.

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

For each of the following functions, find 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}
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 gradient of the tangent to the curve y = x \sqrt{ 2 x + 5} at the point where x = 2.

12

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.

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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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