Solve the equation by completing the square?

Question

x^2+2x-35=0

Answer 1

think of factors of -35 whose difference is +2...

factors of -35 are

1 & -35
-1 & 35
-7 & 5
7 & -5

obviously 7 and -5 are the right factors, so factoring out the equation,

(x-5) (x+7) = 0
x = 5 and -7 :)

Answer 2

Note that it's factorable without it by guessing, but if you must use completing the square:

well, x^2 + 2x + 1 is the square of (x+1)... so we need to add 36 to both sides.

x^2 + 2x -35 + 36 = 36
x^2 + 2x + 1 = 36
(x+1)^2 = 36 ... now sqrt both sides
x+1 = +/-6
x = 5 or -7

Answer 3

(x+7)(x-5)=0
x=-7,5