easier to just solve, but anyway
if you insist on completint the square
4x^2+0x=16
(4x^2+0x)=16
4(x^2+0x)=16
0/2=0, 0^2=16
4(x^2+0x+0-0)=16
4((x+0)^2-0)=16
4(x+0)^2-0=16
4(x+0)^2=16+0
4(x+0)^2=16
divide both sides by 4
(x+0)^2=4
sqrt both sides don't forget to take positive and negative roots
x+0=+/-2
minus 0 from both sides
x=+/-2-0
x=+/-2
x=2 or -2
