How do you complete the square and solve $x^2+3x-28=0$ ?

Question

2929 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2016-11-28T22:31:00

$x =-7$ and $x = 4$

First, to factor the quadratic equation we need to play with integers which multiple to 28: 1,28 and 2,14 and 4,7

Trying combinations of these allows us to rewrite this problem as:

$(x + 7)(x - 4) = 0$

We can now solve for $x + 7 = 0$ and $x - 4 = 0$

$x + 7 = 0 -> x + 7 - 7 = 0 - 7 -> x =-7$

$x - 4 = 0 -> x -4 + 4 = 0 + 4 -> x = 4$

How do you complete the square and solve x^2+3x-28=0x^2+3x-28=0?