Question

已知a、b互为相反数,c、d互为倒数,x=4 (a-2)- (a-3b),y=cd-(c+1)求x

已知a与b互为相反数,c与d互为倒数,x=4(a-2)-(a-3b),y=c^2d(cd+c分之1-1),求4分之x+y - 8分之3x-5y的值

Answer 1

∵a与b互为相反数
∴a+b=0
∵c与d互为倒数
∴cd=1
∴x=4(a-2)-(a-3b)=4a-8-a+3b=3a+3b-8=3(a+b)-8=3×0-8=-8
y=c^2d(cd+1/c-1)=c(cd)(c^2d+1-c)/c=(cd)(c^d+1-c)=1×(c+1-c)=1
∴(x+y)/4-(3x-5y)/8=(-8+1)/4-(-24-5)/8=-7/4+29/8=15/8