How do you solve the quadratic X^2 - 8X + 15 = 0 ?

First factorise (using a "farmer's field", will draw this on whiteboard):=> (X-3)(X-5) = 0Hence using the zero rule (one of the brackets must be equal to 0 if the product is 0),either X-3 = 0 OR X-5=0=> X=3 or X=5Check by substituting back into the original equation:(3)^2 - 8(3) + 15 = 09 - 24 + 15 = 0-15 + 15 = 0 (correct)and(5)^2 - 8(5) +15 = 025 - 40 +15 = 0-15 + 15 = 0 (correct).

SJ
Answered by Simone J. Maths tutor

2525 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

You have a cubiod of dimension 2.2m by 1.8m by 2.0m, you have a pole of length 3m. Will the pole fit into the cuboid?


How do I calculate negative powers?


The perimeter of a right-angled triangle is 72 cm. The lengths of its sides are in the ratio 3 : 4 : 5 Work out the area of the triangle.


Let f(x) = x^2 - 1. A vertical translation of 3 and a horizontal translation of -2 is applied. Write the new function g(x) in the form g(x) = ax^2 + bx + c


We're here to help

contact us iconContact ustelephone icon+44 (0) 203 773 6020
Facebook logoInstagram logoLinkedIn logo

MyTutor is part of the IXL family of brands:

© 2025 by IXL Learning