topic badge

1.05 Quadratic formula

Worksheet
Properties of the discriminant
1

Below is the result after using the quadratic formula to solve an equation:

m = \dfrac{- \left( - 10 \right) \pm \sqrt{ - 1 }}{8}

What can be concluded about the solutions of the equation?

2

How many real solutions do the following equations have?

a

\left(x - 4\right)^{2} = 0

b

x^{2} = 9

3

For the following equations:

i

Find the value of the discriminant.

ii
State the number of real solutions for the equation.
a

x^{2} + 6 x + 9 = 0

b

4 x^{2} - 6 x + 7 = 0

c

2 x^{2} - 2 x = x - 1

4

Consider the equation x^{2} + 22 x + 121 = 0.

a

Find the value of the discriminant.

b

State whether the solutions to the equation are rational or irrational.

5

State whether each of the following equations have any real solutions:

a
- x^{2} - 8 x - 16 = 0
b
- 2 x^{2} + 5 x - 6 = 0
c
- x^{2} + 6 x + 1 = 0
6

For the following equations:

i

Find the discriminant.

ii
Describe the nature of the roots using terms such as:
  • Real or not real

  • Rational or irrational

  • Equal or unequal

a

5 x^{2} + 4 x + 8 = 0

b

4 x^{2} + 4 x - 6 = 0

c

4 x^{2} - 4 x + 1 = 0

7

Consider the equation x^{2} - 8 x - 48 = 0.

a

Find the discriminant.

b

Describe the nature of the roots.

c

Find the solutions of the equation.

8

Consider the equation x^{2} + 14 x + 39 = 0.

a

Find the discriminant.

b

Describe the nature of the roots.

c

Find the exact roots of the equation.

9

To find the x-intercepts of a particular parabola, Katrina used the quadratic formula and found that b^{2} - 4 a c = - 5. How many x-intercepts does the parabola have?

10

For a particular quadratic equation b^{2} - 4 a c = 0. What can be said about the solutions of the quadratic equation?

11

The solutions of a quadratic equation are 9 and - 9.

What can be said about the value of b^{2} - 4 a c?

12

Consider the following quadratic equations in terms of x. Find an expression for the discriminant of the equation:

a

m x^{2} + 3 x - 2 = 0

b

x^{2} + 5 x + p - 5 = 0

13

Find the values of n for which x^{2} - 8 n x + 1296 = 0 has one solution.

14

Consider the equation in terms of x:

m x^{2} - 3 x - 5 = 0
a

Given that it has two unique solutions, determine the possible values of m.

b

There is one value of m that must be eliminated from the range of solutions found in the previous part. What is this value?

15

Consider the equation in terms of x:

m x^{2} + 2 x - 1 = 0

Given that it has two solutions, determine the possible values of m.

16

The graph of y = m - 9 x - 3 x^{2} has no x-intercepts.

a

Solve for the possible values of m.

b

What is the largest possible integer value of m?

17

Solve for the value(s) of k for which y = 4 x^{2} - 4 x + k - 15 just touches the x-axis.

18

The equation \left(m + 4\right) x^{2} + 2 m x + 2 = 0 has a single solution. Find the possible values of m.

19

Find the range of values of k for which y = x^{2} - \left(k - 2\right) x + k - 2 has two x-intercepts.

20

For the following equations:

i

Find the discriminant in terms of k.

ii

Find the value of k for when the equation has equal solutions.

iii

Find the value of k for when the equation has real solutions.

iv

Find the value of k for when the equation has no real solutions.

v

Find the value of k for when the equation has real and distinct solutions.

a

2 x^{2} + 8 x + k = 0

b

\left(k + 4\right) x^{2} + 10 x + 3 = 0

Quadratic formula
21

Is the following statement true or false?

'Any quadratic equation that can be solved by completing the square can also be solved by the quadratic formula.'

22

The standard form of a quadratic equation is a x^{2} + b x + c = 0. Find the values of a, b and c in the quadratic equations below:

a

x^{2} + 7 x + 10 = 0

b

4 x^{2} + 3 x = 5

c

3 x^{2} - 8 x + 2 = 9 x - 7

23

Solve the following equations using the quadratic formula:

a

x^{2} + 11 x + 28 = 0

b

x^{2} - 5 x + 6 = 0

c

4 x^{2} - 7 x - 15 = 0

d

x^{2} + 5 x + \dfrac{9}{4} = 0

e

- 6 - 13 x + 5 x^{2} = 0

f
x^2+8x+16=0
g
x^2+12x+36=0
h
x^2-4x+4=0
i
x^2-10x+25=0
j
x^2+7x+13=0
k
-x^2-3x-5=0
l
x^2-4x+5=0
m
-x^2-5x-8=0
n
4x^2+20x+25=0
o
4x^2-28x+49=0
p
16x^2-24x+9=0
q
64x^2+16x+1=0
r
2x^2-6x+5=0
s
-2x^2+3x-2=0
t
3x^2+7x+7=0
u
5x^2-2x+1=0
24

Solve the following equations using the quadratic formula. Leave your answers in surd form.

a

x^{2} - 5 x - 2 = 0

b

4 x^{2} - x - 10 = 0

c

- 2 x^{2} - 15 x - 4 = 0

25

Solve the following equations using the quadratic formula. Round your answers to one decimal place.

a

1.8 x^{2} + 5.2 x - 2.3 = 0

b

x^{2} + 7 x - 3 = 0

c

3 x \left(x + 4\right) = - 3 x + 4

26

Consider the equation x \left(x + 9\right) = - 20.

a

Solve it by the method of factorisation.

b

Check your solution by solving it using the quadratic formula.

27

Using the quadratic formula, the solutions to a quadratic equation of the form

ax^2 + bx + c = 0 are given by: x = \dfrac{- 5 \pm \sqrt{5^{2} - 4 \times \left( - 7 \right) \times 10}}{2 \times \left( - 7 \right)}

a

Find the values of a, b and c.

b

Write down the quadratic equation that has these solutions.

Applications
28

An object is launched from a height of 90 feet with an initial velocity of 131 feet per second. After x seconds, its height (in feet) is given by h = - 16 x^{2} + 131 x + 90

Solve for the number of seconds, x, after which the object is 20 feet above the ground. Give your answer to the nearest tenth of a second.

29

Consider a right-angled triangle with side lengths x units, x + p units and x + q units, ordered from shortest to longest. No two sides of this triangle have the same length.

a

How many real values of x are possible? Explain your answer.

b

Find the value of x when q = 2 p. Give your answer in terms of p.

Sign up to access Worksheet
Get full access to our content with a Mathspace account

Outcomes

1.2.2.3

solve quadratic equations algebraically using factorisation, the quadratic formula (both exact and approximate solutions), and completing the square and using technology

1.2.2.6

determine turning points and zeros of quadratic functions with and without technology

What is Mathspace

About Mathspace