①2x^2-(x+2)(x-2)-(x+1)^2
=2x^2-(x^2-4)-(x^2+2x+1)
=2x^2-x^2+4-x^2-2x-1
=-2x+3
②（2x-y)(4x^2+y^2)(2x+y）
=（2x-y)(2x+y）(4x^2+y^2)
=(4x^2-y^2)(4x^2+y^2)
=16x^4-y^4
③（-2xy^2）(1/4x^3y)^2
=（-2xy^2）(1/16x^6y^2)
=-1/8 x^7 y^4
④4a^2x^2(-2/5a^4x^2y^3)÷(-1/5a^5x^4y^2)
=-8/5a^4 x^4 y^3)÷(-1/5a^5x^4y^2)
=8a^(-1) y