А) (1+3a) + (a² - 2a) = 1+3a +a² -2a = a²+a+1
б) (2x²+3x) +(-x+4) = 2x²+3x-x+4 = 2x²+2x +4
в) (y²-5y) + (5y-2y²) = y²-5y+5y-2y² = -y²
г) (b²-b+7) - (b²+b+8) = b²-b+7 -b²-b-8 = -2b-1
д) (8n³ - 3n²) - (7+8n³-2n²) = 8n³-3n²-7-8n³+2n² = -n²-7
е) (a²+5a+4) - (a²+5a-4) = a²+5a+4 - a²-5a+4 = 8