4x^2+4x+1=16

4 x^2 + 4 x - 15 = 0

x = [ -4 +/- sqrt(256) ]/8
= [ -4 +/- 16] / 8
=12/8 or 20/8
= 3/2 or -5/2
or
(2x-3)(2x+5) = 0