1.原式=-(1/2×2^4)×(x^2×x^5)×(y^3×y^5)
=-2^3×x^7×y^8
=-8x^7y^8
2.原式=(x-y)^3×(x-y)^2×[-(x-y)^5]
=-(x-y)^3×(x-y)^2×(x-y)^5
=-(x-y)^10
3.原式=2^3×2^3×2^5×2^8
=2^(3+3+5+8)
=2^19