Ответ:

1/3*(3/10v-6/10)=1/3*3/10v-1/3*6/10= 1/10v-2/10

1/4*(4/10v-8/10)=1/4*4/10v-1/4*8/10= 1/10v-2/10

1/10v-2/10-(1/10v-2/10)=1/10v-2/10-1/10v+2/10= 0