x^2+4^2=(x+2)^2
x^2 + 4^2 = (x + 2)^2
x^2 + 16 = x^2 + 4x + 4 subtract x^2 from both sides
16 = 4x + 4 divide through by 4
4 = x + 1 subtract 1 from both sides
3 = x
literally ty sm