(-5x⁴ +2x² -x+3)+(5x⁴ -2x²+x-3) = -5x⁴ +2x² -x+3+5x⁴ -2x²+x-3 = -5x⁴+5x⁴+2x²-2x²-x+x+3-3 = 0
Ответ: 0