Question

合并同类项求值已知：a=-2x平方+y,b=x平方-2y1.化简a-b2.当x=1 y=2时 求a+b的值

Answer 1

∵a=2x²+y

b=x²-2y

∴a-b=2x²+y-(x²-2y)

=x²+3y

当x=1 y=2时,a+b=2x²+y+x²-2y

=3x²-y

=3×（1）²-2

=1