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

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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. 

(x-3)(x-5)=0

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

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