How do you solve x^2+15x+56=0?
1 Answer
Mar 27, 2016
x = -7 orx = -8
Explanation:
Find a pair of factors of
The pair
Hence:
0 = x^2+15x+56 = (x+7)(x+8)
So:
x = -7 orx = -8
Alternative method
I will use the difference of squares identity:
a^2-b^2 = (a-b)(a+b)
with
First multiply the whole equation by
0 = 4x^2+60x+224
=(2x+15)^2-225+224
=(2x+15)^2-1^2
=((2x+15)-1)((2x+15)+1)
=(2x+14)(2x+16)
=(2(x+7))(2(x+8))
=4(x+7)(x+8)
Hence