Question

某同学做一道数学题，“已知两个多项式A、B，B=4x^2-5x-6,试求A+B”，这位同学把A+B看成A-B

,结果求出答案是-7x^2+10x+12,那么A+B的正确答案是多少？

Answer 1

因为,错把A+B看成A-B，实际计算出A-B=-7x^2+10x+12
那么,A+B=(A-B)+2B
=-7x^2+10x+12+2*(4x^2-5x-6)
=-7x^2+10x+12+8x^2-10x-12
=x^2
所以A+B=x^2

Answer 2

A+B＝A-B＋2B，而A-B＝-7x^2+10x+12，B＝4x^2-5x-6
所以
A+B＝-7x^2+10x+12＋2（4x^2-5x-6）
＝x^2

Answer 3

A+B
=(A-B)+2B
=-7x^2+10x+12+2(4x^2-5x-6)
=-7x^2+10x+12+8x^2-10x-12
=X^2

Answer 4

A-B=-7x^2+10x+12
A=-7x^2+10x+12+B
=-7x^2+10x+12+4x^2-5x-6
=-3x^2+5x+6

A+B=-3x^2+5x+6+4x^2-5x-6
=x^2