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# Need help with this question watch

1. Find, as surds, the roots of the equation:

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

2. (Original post by Chrisrc)
Find, as surds, the roots of the equation:

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

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.
3. 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?
4. (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?
5. I tried it with both 'completing the square' and 'ax^2 + bx + c" formula and got the same answer
6. (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?
7. 2(x+1)(x-4) - (x-2)^2 = 0
8. (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?
9. Oooh sarry, I got x^2 -10x - 4 = 0
10. (Original post by Chrisrc)
Oooh sarry, I got x^2 -10x - 4 = 0
It should be

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.
11. What do you get when you expand
2(x+1)(x-4) and when you expand -(x-2)^2
12. (Original post by Chrisrc)
What do you get when you expand
2(x+1)(x-4) and when you expand -(x-2)^2
13. Oh I see I got that too but I didn't put the x^2 - 4x + 4 in brackets and times it by -1... Thanks for your help

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