解
a²+5a-2a²-3a²-5a-1
=(a²-2a²-3a²)+(5a-5a)-1
=-4a²-1
=-4×(-1/2)²-1
=-1-1
=-2
x²+4x-2x²-5x+3x²-2
=(x²-2x²+3x²)+(4x-5x)-2
=2x²-x-2
=2×4-2-2
=4
3pq-4/5m-4pq
=-pq-4/5m
=-(1/3)×(-3/2)-4/5×5
=1/2-4
=-7/2
2x²-x-4+3x-4²——这个吗
=2x²+2x-20
=2×(-1/2)²+2×(-1/2)-20
=1/2-1-20
=-39/2