36x2 + 96xy + 64y2
note that 36 and 64 are both perfect squares. So try
(6x+8y)^2
note that 2(6*8) = 96, so we are correct.
Expanding the square, we get:
(6x+8y)^2 = (6x)^2 + 2(6x)(8y) + (8y)^2
= 36x^2 + 96xy + 64y^2
Therefore, 36x^2 + 96xy + 64y^2 = (6x+8y)^2.