(·黑龙江牡丹江)某商品每件标价为150元,若按标价打8折后,再降价10元销售,仍获利10%,则该商品每件的进价为 元.
(1)(3a-4b)()=9a2-16b2;(2)(4+2x)()=16-4x2; (3)(-7-x)()=49-x2;(4)(-a-3b)(-3b+a)=_______.
计算: (1)(a+1)(a-1)=_________;(3)(-a+1)(a+1)=________; (3)(-a+1)(a+1)=________;(4)(a+1)(-a-1)=_______.
用字母表示平方差公式为:___________.
计算:(3x-y)(x+2y)=________.
计算:(x-3)(3x-4)=_________;