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iGCSE (2021 Edition)

11.08 Using the first derivative

Worksheet
Increasing and decreasing functions
1

Determine whether following statements describe a maximum or a minimum turning point:

a

A point where the curve changes from increasing to decreasing.

b

A point where the curve changes from decreasing to increasing.

2

Consider the function

f \left( x \right) = - \left(x - 4\right)^{3} + 7 shown:

a

What is the x-coordinate of the stationary point?

b

State the domain for which f \left( x \right) is decreasing.

1
2
3
4
5
6
7
8
x
-1
1
2
3
4
5
6
7
8
9
y
3

For each of the functions graphed below:

i

State the x-coordinate of the stationary point(s).

ii

State the domain for which f \left( x \right) is increasing.

iii

State the domain for which f \left( x \right) is decreasing.

a
-5
-4
-3
-2
-1
1
2
3
4
5
x
-5
-4
-3
-2
-1
1
2
3
4
5
y
b
-5
-4
-3
-2
-1
1
2
3
4
5
x
-5
-4
-3
-2
-1
1
2
3
4
5
y
c
-12
-10
-8
-6
-4
-2
2
4
6
x
-4
-2
2
4
6
8
y
d
-7
-6
-5
-4
-3
-2
-1
1
2
3
4
5
x
-7
-6
-5
-4
-3
-2
-1
1
2
3
y
4

Consider the function f \left( x \right) shown:

a

State the x-coordinate of the stationary point.

b

State the domain for which f \left( x \right) is increasing.

c

State the domain for which f \left( x \right) is decreasing.

d

State the domain for which f \left( x \right) is constant.

-7
-6
-5
-4
-3
-2
-1
1
2
3
x
-5
-4
-3
-2
-1
1
2
3
4
5
y
Stationary points
5

For each of the following functions:

i

Find the derivative.

ii

Find the coordinates of any stationary points.

iii

Classify the stationary points.

a
y = - 6 x^{2} + 84 x - 29
b
y = x^{3} - 21 x^{2} + 144 x - 19
c
f \left( x \right) = \left(x + 3\right)^{2} \left(x + 6\right)
d
f \left( x \right) = \left(x + 5\right)^{3} + 4
e
f \left( x \right) = - \dfrac{x^{3}}{3} + \dfrac{13 x^{2}}{2} - 30 x + 10
f
f \left( x \right) = \left( 4 x + 5\right) \left(x + 1\right)
6

Consider the equation of the parabola y = 3 x^{2} - 18 x + 24.

a

Find the x-intercepts.

b

Find the y-intercept.

c

Find \dfrac{dy}{dx}.

d

Find the coordinates of any stationary points.

e

Classify the stationary point.

f

Sketch the graph of the parabola.

7

For each of the following quadratic equations:

i

Find the coordinates of the turning point.

ii

Classify the turning point.

a
y = x^{2} - 4 x + 6
b
y = 5 + x - x^{2}
c
y = 2 x^{2} - 8 x + 7
d
f \left( x \right) = 3 x^{2} - 54 x + 241
8

Consider the function f \left( x \right) = 134 - 300 x + 240 x^{2} - 64 x^{3}.

a

Find the derivative.

b

Find the coordinates of the stationary point.

c

Classify the stationary point.

9

Consider the function f \left( x \right) = \left(x^{2} - 9\right)^{2} + 4.

a

Find the derivative.

b

Find the coordinates of the stationary points.

c

Classify the stationary points.

Sketching functions
10

Sketch the linear function for which f \left( 0 \right) = 1 and f' \left( 2 \right) = 3.

11

Sketch a quadratic function, f \left( x \right), that satisfies the following conditions:

a
  • f \left( 0 \right) = - 18
  • f \left( 3 \right) = 0
  • f \left( 6 \right) = 6
  • f' \left( 6 \right) = 0
  • f' \left( x \right) > 0 for x < 6

b
  • f \left( 0 \right) = 16
  • f \left( 2 \right) = 0
  • f \left( 5 \right) = - 9
  • f' \left( 5 \right) = 0
  • f' \left( x \right) < 0 for x < 5

c
  • f \left( 0 \right) = 5
  • f \left( - 2 \right) = 0
  • f' \left( 3 \right) = 0
  • f' \left( x \right) > 0 for x < 3

12

Sketch a cubic function, f \left( x \right), that satisfies the following conditions:

a
  • f' \left( - 5 \right) = 0
  • f' \left( x \right) > 0 for all other values of x.

b
  • f \left( 0 \right) = 7
  • f \left( - 2 \right) = 0
  • f \left( - 4 \right) = - 1
  • f' \left( - 4 \right) = 0
  • f' \left( x \right) > 0 for x < - 4

  • f' \left( x \right) > 0 for x > - 4

c
  • f' \left( 2 \right) = 0
  • f' \left( - 3 \right) = 0
  • f' \left( x \right) < 0 for - 3 < x < 2

  • f' \left( x \right) > 0 elsewhere

13

Sketch a quartic function, f \left( x \right), that satisfies the following conditions:

a
  • f' \left( - 1 \right) = 0
  • f' \left( 4 \right) = 0
  • f' \left( x \right) > 0 for x > 4

  • f' \left( x \right) < 0 elsewhere

b
  • f \left( 0 \right) = 0
  • f' \left( 0 \right) = 0
  • f' \left( 2 \right) = 0
  • f' \left( - 2 \right) = 0
  • f' \left( x \right) > 0 for x < - 2, 0 < x < 2

  • f' \left( x \right) < 0 elsewhere

Using the first derivative
14

The function y = a x^{2} - b x + c passes through the points (5, - 42) and (4, - 66) and has a maximum turning point at x = 3.

a

Find \dfrac{dy}{dx}.

b

Find the value of a

c

Find the value of c.

d

Find the value of b.

15

Consider the cubic function y = x^{3} - a x^{2} + b x + 11, which has stationary points at x=2 and x=10.

a

Find \dfrac{dy}{dx}.

b

Find the value of a.

c

Hence find the value of b.

16

Consider the gradient function f' \left( x \right) = 2 x + 6 graphed below:

a

State the x-intercept of the gradient function.

b

Is the gradient of f \left( x \right) for x > - 3 positive or negative?

c

Is the gradient of f \left( x \right) for x < - 3 positive or negative?

d

What feature of f \left( x \right) does this x-intercept represent?

-4
-3
-2
-1
1
2
3
4
x
-4
-3
-2
-1
1
2
3
4
f'(x)
17

The function f \left( x \right) has a derivative given by f' \left( x \right) = 6 \left(x - 2\right) \left(x - 7\right). A graph of the derivative function is shown:

a

State the x-intercept(s) of the gradient function.

b

What kind of feature is at the point \left(2, 77\right) on the graph of f \left( x \right)?

c

What kind of feature is at the point \left(7, - 48 \right) on the graph of f \left( x \right)?

-8
-6
-4
-2
2
4
6
8
x
-40
-30
-20
-10
10
20
30
40
f'(x)
18

The function f \left( x \right) has a derivative given by f' \left( x \right) = 3 \left(x + 5\right)^{2}. A graph of the derivative function is shown:

a

State the x-intercept(s) of the gradient function.

b

What kind of feature is at the point \left( - 5 , 2\right) on the graph of f \left( x \right)?

-8
-6
-4
-2
2
4
6
8
x
-8
-6
-4
-2
2
4
6
8
f'(x)
19

Consider the gradient function f' \left( x \right) = 12 \left(x + 4\right)^{2} \left(x + 7\right).

a

Graph the gradient function.

b

What kind of feature is at the point \left( - 7 , - 1617 \right) on the graph of f \left( x \right)?

c

What kind of feature is at the point \left( - 4 , - 1536 \right) on the graph of f \left( x \right)?

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Outcomes

0606C14.2

Use the notations f'(x), f''(x), dy/dx, d^2y/dx^2 [=d/dx(dy/dx)].

0606C14.5B

Apply differentiation to stationary points.

0606C14.6

Use the first and second derivative tests to discriminate between maxima and minima.

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