Factorise and solve x^2 - 8x + 15 = 0

The question gives you a hint on how to go about this question - Factorise!!

1) Factorise the left hand side. Find the two numbers which will add to give -8 and multiply to give 15. In this case, -3 and -5. 


2) Each set of brackets can equal 0. If a multiplication is equal to 0, then at least one term must be 0 itself. 

x-3=0, x-5=0

3) Solve the equations. 

x=3 or 5

4) CHECK!! Plug your values of x into the original equation to make sure you are right - an easy way to stop making silly mistakes! 

When x=3, 32-(8x3)+15 = 9-24+15=0  (correct)

When x=5, 52-(8x5)+15 = 25-40+15=0 (correct)


Kieran N. GCSE Maths tutor, GCSE History tutor, GCSE Spanish tutor

10 months ago

Answered by Kieran, a GCSE Maths tutor with MyTutor

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


£20 /hr

Costas Y.

Degree: Electrical & Electronic Engineering (Doctorate) - Imperial College London University

Subjects offered: Maths, Further Mathematics + 1 more

Further Mathematics

“About Me: I am a 3rd year PhD student at Imperial College London studying in the Electrical and Electronic Engineering department. Ambitious and enthusiastic engineer and have a passion for mathematics and electronics. Aside from my...”

MyTutor guarantee

£18 /hr

Ross N.

Degree: Medicine (Bachelors) - Exeter University

Subjects offered: Maths, Chemistry+ 2 more


“About Me: I'm Ross and I'm a Medical Student at the University of Exeter. I strongly believe that science + maths are incredibly interesting and fun subjects when you understand them - I intend to help you do just that. I am a high e...”

£18 /hr

Oliver T.

Degree: Mathematics (Masters) - Edinburgh University

Subjects offered: Maths, Further Mathematics

Further Mathematics

“Hello! I'm currently a 2nd year Mathematics student at the University of Edinburgh with a sturdy passion for all things Mathematics. Not only do I love Maths, I love teaching Maths and helping people with problems. In particular, I en...”

About the author

Kieran N.

Currently unavailable: for regular students

Degree: Spanish and History (Bachelors) - Southampton University

Subjects offered: Maths, History


“About Me I am a first year student at the University of Southampton, studying Spanish and History. Although I eventually chose to follow humanities, I was always split as to what I prefered - at A Level I was so unsure I ended up taki...”

MyTutor guarantee

You may also like...

Posts by Kieran

Factorise and solve x^2 - 8x + 15 = 0

How do I analyse a source?

What is the subjunctive and when should it be used?

Other GCSE Maths questions

Solve this quadractic equation: x^2 - 8x + 15 = 0

How do I factorise x^2 ​- 4?

What is Pythagoras's theorem?

Solve the equation ((2x+3)/(x-4))-((2x-8)/(2x+1))=1

View GCSE Maths tutors


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