3b-2c-[-4a+(c+3b)]+c
=3b-2c-(-4a+c+3b)+c
=3b-2c+4a-c-3b+c
=4a-2c
将a=1/4.c=1/2代入、得、
4a-2c=4×1/4-2×1/2
=1-1
=0