K=3x-(x+7)=3x-x-7=2x-7
L=13-(4x+1)=13-4x-1=12-4x=-4x+12
M=-8-(-2x-3)=-8+2x+3=-5+2x=2x-5
a) K=L+M
2x-7=-4x+12+2x-5
2x-7=-2x+7
2x-7≠-2x+7
b) K+L=M
2x-7+(-4x)+12=2x-5
2x-7-4x+12=2x-5
-2x+5=2x-5
-2x+5≠2x-5
c) K+L+M-0
2x-7-4x+12+2x-5=0
5-5=0
0=0 - tożsamość
Odp. C
