先化简,(1)3(a-1)-(a-5),其中a=2 (2)(a+3b)(a-3b)-(a-b)2,其中a=1/2,b=-1

问题描述:

先化简,
(1)3(a-1)-(a-5),其中a=2 (2)(a+3b)(a-3b)-(a-b)2,其中a=1/2,b=-1

(1)3(a-1)-(a-5)
=3a-3-a+5
=2a+2
=2x2+2
=6
(2)(a+3b)(a-3b)-(a-b)2
=a²-9b²-(a²-2ab+b²)
=a²-9b²-a²+2ab-b²
=-10b²+2ab
=-10x1-2x1/2x1
=-10-1
=-11