数学之美团为你解答
(x+2y)(x-2y) - (2x - y)(-2x-y)
= (x+2y)(x-2y) + (2x-y)(2x+y)
= x² - 4y² + 4x² - y²
= 5x² - 5y²
= 5(x² - y²)
= 5(x+y)(x-y)
x=8,y= -8,x+y =0
∴原式 = 0