3(5a^2b-3an^2)-4(ab^2+2a^2b)其中a=-1/2,b=1/3

题目

3(5a^2b-3an^2)-4(ab^2+2a^2b)其中a=-1/2,b=1/3

答案

3(5a^2b-3ab^2)-4(ab^2+2a^2b)
=15a^2b-9ab^2-4ab^2-8a^2b
=7a^2b-13ab^2
代入a=-1/2,b=1/3,得到
原式=7/4·1/3+13/2·1/9
=7/12+13/18
=47/36