先化简,再求值 ⒈2(Xy+Xy)-3(Xy-xy)-4Xy,其中X=1,y=-1
问题描述：
先化简,再求值 ⒈2(Xy+Xy)-3(Xy-xy)-4Xy,其中X=1,y=-1
先化简,再求值
⒈2(Xy+Xy)-3(Xy-xy)-4Xy,其中X=1,y=-1
⒉1/2ab-5aC-(3ac b)+(3aC-4a C),其中a=-1,b=2,C=-2
答
1.2(Xy+Xy)-3(Xy-xy)-4Xy=2*2xy-0-4xy=4xy-4xy=02.1/2ab-5aC-(3ac b)+(3aC-4a C)=1/2ab-5ac-3acb-ac=1/2ab-6ac-3acb=1/2ab-3ac(2+b)当a=-1,b=2,c=-2时1/2ab-3ac(2+b)=1/{2(-1)*2}-3(-1)（-2）（2+2）=1/(-4)-24=-0.2...