(3a-4b)²-(3a+b)(3a-b)=------------

问题描述:

(3a-4b)²-(3a+b)(3a-b)=------------

=(3a-4b)²-(3a-b)²=(3a-4b+3a-b)(3a-4b-3a+b)=(6a-5b)(-3b)=-18ab+15b²