因式分解因式分解：(x+2)(x-2)+y(4-y)请高手指教.不然可能看不懂.

直接展开得
x^2-4+4y-y^2
=x^2-y^2-4+4y
=x^2-(y^2-4y+4)
=x^2-(y-2)^2
=(x+y-2)(x-y+2) 如果还不懂可以问我

(x+2)(x-2)+y(4-y)
=x^2-4+4y-y^2
=x^2-(y^2-4y+4)
=x^2-(y-2)^2
=(x+y-2)(x-y+2)