Factorise and solve x^2 – 8x + 15 = 0

This equation is of the form ax2 + bx + c = 0 (where a = 1, b = -8 and c = 15). To help solve it, find two numbers that add to give the value of b (the 'sum') and also when multiplied together give the same answer as a*c (the 'product'). 

For this equation, the sum = -8 and the product = 15.

Because the sum is negative and the product is positive we're looking for two negative numbers.

In this case they are -3 and -5, so the factorised equation would be: (x - 3)(x - 5) = 0.

In the factorised equation, the two bracket terms are multiplied together, so to solve the equation, make one of the brackets equal zero. 

The two 'roots' of the equation, i.e. the values of x that make the equation true, are x = 3 and x = 5.


Andrew B. GCSE Chemistry tutor, A Level Chemistry tutor, GCSE Maths t...

1 year ago

Answered by Andrew, who tutored GCSE Maths with MyTutor

Still stuck? Get one-to-one help from a personally interviewed subject specialist


£18 /hr

Guido B.

Degree: Aeronautical Engineering (Masters) - Imperial College London University

Subjects offered:Maths, Science+ 3 more

Further Mathematics

“Expert tuition from an expert. A second year Uni student who's completed the hassle of GCSEs and A Levels, and can teach you the easy way to pass and succeed!”

£30 /hr

Piyush S.

Degree: Electronics Engineering (Doctorate) - Imperial College London University

Subjects offered:Maths


“I am an experienced and passionate tutor for Maths and Science (Physics in particular). Throughout my higher education, I have been wondering about how Mathematics acts as a tool to model and simplify the complicated concepts of the P...”

Roma V. A Level Maths tutor, 13 Plus  Maths tutor, GCSE Maths tutor, ...
£24 /hr

Roma V.

Degree: Mathematics, Operational Research, Statistics and Economics (Bachelors) - Warwick University

Subjects offered:Maths, Further Mathematics + 1 more

Further Mathematics

“Top tutor from the renowned Russell university group, ready to help you improve your grades.”

About the author

Andrew B.

Currently unavailable: until 01/09/2016

Degree: Chemistry (Masters) - Oxford, Keble College University

Subjects offered:Maths, Chemistry


“Top tutor from the renowned Russell university group, ready to help you improve your grades.”

MyTutor guarantee

You may also like...

Posts by Andrew

Explain how electricity is conducted through a metal. To gain full marks your answer must include a description of the structure and bonding in a metal.

Factorise and solve x^2 – 8x + 15 = 0

Given that 5cos^2(x) - cos(x) = sin^2(x), find the possible values of cos(x) using a suitable quadratic equation.

Identify the dehydration product or products of a) ethanol, b) button-2-ol

Other GCSE Maths questions

​What's the difference between the mean, median and mode? Why are there so many different types of average?!

Can you run through the quadratic equation(including the sketch and algebra).

A circle with centre C has equation x^2 + y^2 + 2x - 6y - 40 = 0. Express as (x - a)^2 + (y - b)^2 = d.

What is the solution to the system of equations defined by (1) x+2y = 4 and (2) y+2x = 6?

View GCSE Maths tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss