已知a+b=负四分之一,求代数式3(a+b)-5a-5b+7的值,要过程

问题描述:

已知a+b=负四分之一,求代数式3(a+b)-5a-5b+7的值,要过程

a+b=-1/4,求代数式3(a+b)-5a-5b+7的值
3(a+b)-5a-5b+7
=3(a+b)-5(a+b)+7
=-2(a+b)+7
=-2(-1/4)+7
=1/2+7
=7.5已知x+y=-2,试计算1/2(x+y)+4(x-y)-3(x-y)-x+y的值已知x+y=-2,试计算1/2(x+y)+4(x-y)-3(x-y)-x+y1/2(x+y)+4(x-y)-3(x-y)-x+y=1/2(x+y)+(x-y)-x+y=1/2(x+y)+x-y-x+y=1/2(x+y)=1/2(-2)=-1