a^6b^3×（-2a^3b^-2c)计算 （9x^y-6xy^2）×3xy计算 51^2×50-49^2×50 （18a^2b-9a^5b^2)×（-3ab）

a^6b^3×（-2a^3b^-2)?=-2a^(6+3)b^(3-2)=-2a^9b;
（9x^2y-6xy^2）×3xy?=27x^(2+1)y^(1+1)-18x^(1+1)y^(2+1）=27x^3y^2-18x^2y^3;
51^2×50-49^2×50 =50x(51²-49²)=50x(51+49)x(51-49)=50x100x2=10000;
（18a^2b-9a^5b^2)×（-3ab）=-54a^(2+1)b^(1+1)+27a^(5+1)b^(2+1)）=-54a^3b^2+27a^6b^3;