如果是 (x^2+4)^2+8x(x^2+4)+16x^2
(x^2+4)^2+8x(x^2+4)+16x^2
=(x^2+4)^2+2*4x(x^2+4)+ (4x)^2
=(x^2+4+4x)^2
=(x+2)^4