How would you solve a quadratic equation by factorising?

Solve the equation :  x2 - 8x + 15

The first step is to factorise the quadratic equation.

1. You must find two numbers which will add to give -8 and multiply to give 15. 

The numbers that would do this are -5 and -3. 

Therefore (x-5) (x-3). To check whether this is correct, you can expand the brackets and it should give you the equation you first started with. 

The second step is to find the value of x.

2. For this you must equate each bracket to 0. 

(x-5)= 0       and   (x-3)=0

Now solve : x = 5    and   x= 3

The third step is subsitution 

3. Finally to check this is correct. Substitute the values of x into the equation.

 x2 - 8x + 15

-Subsitute x =5

52-8 x 5 +15 = 0

25-40+15 = 0 

-Subsitute x=3

3- 8 x 3 +15 = 0

9-24+15=0 

These 3 simple steps will help you solve any quadratic equation. 

AG
Answered by Angelin G. Maths tutor

4513 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

£3000 is invested for 2 years at 3.8% per annum compound interest. What is the total interest earned over the 2 years?


Solve x^2+5x+6=0 by factorising


A right-angled triangle has side lengths of 4cm and 3cm. What is the length of its hypotenuse?


At the supermarket, Ben buys 5 apples and 3 pears, at a total cost of £3.70. Jenny buys 6 apples and 6 pears, costing £5.40. Construct two simultaneous equations to work out the price, in pence, of apples and pears.


We're here to help

contact us iconContact usWhatsapp logoMessage us on Whatsapptelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

© MyTutorWeb Ltd 2013–2025

Terms & Conditions|Privacy Policy
Cookie Preferences