第一题:-(3a的2次方-b) (b+3a的2次方)用平方差公式计算!快啊.

问题描述:

第一题:-(3a的2次方-b) (b+3a的2次方)用平方差公式计算!快啊.
第二题:(7m+2n) (-7m+2n).

-(3a的2次方-b) (b+3a的2次方)
=(b-3a的2次方) (b+3a的2次方)
=b^2-(3a^2)^2
=b^2-9a^4
(7m+2n) (-7m+2n)
=(2n+7m)(2n-7m)
=(2n)^2-(7m)^2
=4n^2-49m^2