先化简再求值(a-2b)(3a-2b)-3(a-b)(a+3b),其中a=-(1/2),b=1

先化简再求值(a-2b)(3a-2b)-3(a-b)(a+3b),其中a=-(1/2),b=1
先化简再求值(a-2b)(3a-2b)-3(a-b)(a+3b),其中a=-(1/2),b=1

先化简再求值(a-2b)(3a-2b)-3(a-b)(a+3b),其中a=-(1/2),b=1
(a-2b)(3a-2b)-3(a-b)(a+3b)
=3a²-2ab-6ab+4b²-3(a²+3ab-ab-3b²)
=3a²-8ab+4b²-3(a²+2ab-3b²)
=3a²-8ab+4b²-3a²-6ab+9b²
=13b²-14ab
=b(13b-14a)
=1X(13X1-14X(-1/2))
=13+7
=20

(a-2b)(3a-2b)-3(a-b)(a+3b)
=3a^2-8ab+4b^2-(3a^2+6ab-9b^2)
= -14ab+13b^2
= -14(-1/2)(1)+13*1^2
= 7+13
=20