先化简,后求值:5a³-(3b²+5a³)+(4b²+2ab),其中a=-1,b=1/2

问题描述:

先化简,后求值:5a³-(3b²+5a³)+(4b²+2ab),其中a=-1,b=1/2

5a³-(3b²+5a³)+(4b²+2ab)
=5a³-3b²-5a³+4b²+2ab
=5a³-5a³+4b²-3b²+2ab
=b²+2ab
=(1/2)²+2*(-1)*1/2
=1/4-1
=-3/4

5a³-(3b²+5a³)+(4b²+2ab)
=b²+2ab
当a=-1,b=1/2时,原式=1/4-1=-3/4