Verified answer

1) a²+2a-7-a²+4a+9= 6a+2

2) 6x³y-9x²y²+21x²y

3) x³+9x²-2x²-18x= x³+7x²-18x

4) x⁴-10x²+25+10x²= x⁴+25

Ответ:

1) a2+4a+2

2) 6x3y-9x2y2+21x2y

3) x3+7x2-18x

4) x4+25