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Chrisrc

Find, as surds, the roots of the equation:

2(x+1)(x-4) - (x-2)^2=0

Whats the answer?

Reply 1

Mr M

Study Forum Helper

Original post by Chrisrc

Find, as surds, the roots of the equation:

2(x+1)(x-4) - (x-2)^2=0

Whats the answer?

This isn't a homework service.

Expand the brackets (be careful with signs when performing the subtraction) then solve the resulting quadratic by completing the square or by using the quadratic formula.

Reply 2

Chrisrc

I got 5+- square root 29 but my book says it's 1+- square root 13, I can't see how it got that answer?

Reply 3

Mr M

Study Forum Helper

Original post by Chrisrc

I got 5+- square root 29 but my book says it's 1+- square root 13, I can't see how it got that answer?

The book is right. What quadratic did you get?

Reply 4

Chrisrc

I tried it with both 'completing the square' and 'ax^2 + bx + c" formula and got the same answer

Reply 5

Mr M

Study Forum Helper

Original post by Chrisrc

I tried it with both 'completing the square' and 'ax^2 + bx + c" formula and got the same answer

I'll ask again. What was the quadratic you were trying to solve?

Reply 6

Chrisrc

2(x+1)(x-4) - (x-2)^2 = 0

Reply 7

Mr M

Study Forum Helper

Original post by Chrisrc

2(x+1)(x-4) - (x-2)^2 = 0

Blimey. This is hard work. What did you get after you expanded the brackets and collected like terms?

Reply 8

Chrisrc

Oooh sarry, I got x^2 -10x - 4 = 0

Reply 9

Mr M

Study Forum Helper

Original post by Chrisrc

Oooh sarry, I got x^2 -10x - 4 = 0

It should be

x^2-2x-12=0

If you look back to my first post I told you to be careful when subtracting. You weren't careful. There are subtractions of negative numbers to deal with.