Ответ:

1) 2x²+7xy-5x²-11xy+3y² = -4xy

2) -(8c²+3c)+(-7c²-11c+3)-(3c²-4) = -8c²-3c-7c²-11c+3-3c²+4 = -18c²-14+7

3) x(x³+x²+x)-x²(x³+x²+x) = x⁴+x³+x²-x⁵-x⁴-x³ = x²-x⁵

4) -5x⁴(2x-x³)+10x⁵ = -10x⁵+5x⁷+10x⁵ = 5x⁷

5) (x³+2y)(x²-2y)-(x²+2y)(x³-2y) = x⁵-2x³y+2x²y-4y²-x⁵+2x²y-2x³y+4y² = -4x³y+4x²y