a) 2x + x - 3x = 0
b) - 2m - 2a + 3a - 2m = -4m + a = -4 * (-1) + 1 = 4 + 1 = 5
[tex]c) 4c^{2}-2a+5c^{2}+6-5a = 9c^{2}-7a+6 = 9 * (-1)^{2}-7*2+6 = 9 - 14+6=1[/tex]
[tex]d)-9xy+8x^{2}y-xy^{2}-7x^{2}y+4= -9xy+x^{2}y-xy^{2}+4 = -9*1*(-1) + 1^{2}*(-1)-1*(-1)^{2}+4=9-1-1+4=11[/tex]
:)