但我还要再麻烦你.（3a+2b-c)(2b-3a+c),(a+b)^2+15ab-(a-b)^2,621^2-769x474-148^2急用,请快,

Question

但我还要再麻烦你.（3a+2b-c)(2b-3a+c) ,(a+b)^2+15ab-(a-b)^2 ,621^2-769x474-148^2
急用,请快,

Answer 1

（3a+2b-c)(2b-3a+c)=(2b)^2-(3a-c)^2=4b^2 -(9a^2 -6ac +c^2)=4b^2 -9a^2 +6ac -c^2
(a+b)^2+15ab-(a-b)^2=[(a+b)^2 -(a-b)^2]+15ab=[(a+b)+(a-b)][(a+b)-(a-b)]+15ab=(2a)x(2b)+15ab=19ab
621^2-769x474-148^2=(621^2 - 148^2) -769x474=(621 + 148)(621 - 148) -769x474=769x473-769x474=769x(473-474)= -769