Question

某同学做一道数学题，误将求‘A-B’看成求‘A+B’，结果求出的答案是x^2-x+2.已知A=2x^2-x-5,请正确求出

A-B

Answer 1

B=(x²-x+2)-(2x²-x+5)
=-x²+7
A-B=(2x²-x+5)-(-x²+7)
=3x²-x-2

Answer 2

因为算成加,所以B为x²-x+2-(2x²-x-5)=7-x² A+B为2x²-x-5-(7-x²)=3x²-x-12