Solve the quadratic equation: x^2 - 2x - 15 = 0

To solve this, you need to find two factors of -15 that total to give -2. The solution we're looking for is of the for (x + something) (x + something)=0, as you can then solve each bracket to get two results for x.Since the 'c' part (remember Ax2 + Bx + C = 0 is the general equation) is negative, we know one factor minus another equals 2. What factors of 15 are there? Well, there aren't many; 1,3,5,15 are the only ones. 5-3 gives us 2, which is what we want!If we had 5 and -3 to replace the two 'something's in our solution, we would have a total of 2x. But we want -2x, so we must use -5 and +3 in our solution. Then, we have (x-5)(x+3)=0. Almost done!As each bracket must =0, as they multiply to give 0, we know x-5=0 and x+3=0. Solving those gives x=5 and x=-3; done!

JH
Answered by James H. Maths tutor

4019 Views

See similar Maths GCSE tutors

Related Maths GCSE answers

All answers ▸

1/7 + 5/3x


Fully simplify: (y^2 x y^5) / y^3


The circle c has equation x^2+ y^2 = 1. The line l has gradient 3 and intercepts the y axis at the point (0, 1). c and l intersect at two points. Find the co-ordinates of these points.


Work out: 0.7 + 3/5


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