已知:a+b=0,cd=1,x=4(a-2)-(a-3b),y=c²d+d²-(d/c+c-1),求(x+y)/4-(3x-5y)/8的值

题目

已知:a+b=0,cd=1,x=4(a-2)-(a-3b),y=c²d+d²-(d/c+c-1),求(x+y)/4-(3x-5y)/8的值

答案

x=4a-8-a+3b=3(a+b)-8=-8
y=c+d²-(d/c+c-1)=d²-d/c+1=(cd²-d)/c+1=1 " cd²-d=d(cd-1)=0 "
(x+y)/4-(3x-5y)/8=(2x+2y-3x+5y)/8=(7y-x)/8=15/8