20a^3×(5a)^2 = -0,4x^5×(2x^3)^4 = (-c^3)^2×12c^6 = (3x^6y^3)^4×(-1/81xy^2) = (-2/3ab^5)×18a^5b =

20a^3×(5a)^2 = 500a^5

-0,4x^5×(2x^3)^4 = -4096x^17

(-c^3)^2×12c^6 = 144c^12

(3x^6y^3)^4×(-1/81xy^2) = -1/729x^9y^10

(-2/3ab^5)×18a^5b = -12ab^6