1.已知m+n=3,mn=2,求—3(1/3n—mn)+2(mn—1/2m）.

题目

1.已知m+n=3,mn=2,求—3(1/3n—mn)+2(mn—1/2m）.
2.已知y=ax^5+bx^3+cx—1,当x=-2时,y=5,求当x=2,y的值.

答案

1.
—3(1/3n—mn)+2(mn—1/2m）＝（3mn^2-1）/n + （2nm^2-1）/m
=5mn-(m+n)/(mn)=5x2-3/2=10-1.5=8.5
2.
当x=-2,y=a(-2)^5+b(-2)^3+c(-2)—1＝－（a2^5+b2^3+c2）-1 =5
所以a2^5+b2^3+c2=-5-1＝-6
当x=2,y=a2^5+b2^3+c2—1＝-6-1＝-7