Question

已知x+y=-4试计算多项式0.5(x+y)+4(x-y)-3(x-y)-1.5(x+y)-x+y的值

Answer 1

解原式=(0.5-1.5)(x+y)+(4-3-1)(x-y)

=-1(x+y)

把（x+y）=-4代入-1（x+y）得4