1.多项式x^2+6x+y^2-8y+30有最小值时,x=?y=?2.若x^2+2x-1=0,那么5x^2+10x-3=?

问题描述:

1.多项式x^2+6x+y^2-8y+30有最小值时,x=?y=?2.若x^2+2x-1=0,那么5x^2+10x-3=?

1.x^2+6x+y^2-8y+30
=(x+3)²+(y-4)²+5
当x=-3;y=4时,原式有最小值5
2.若x^2+2x-1=0
x²=-2x+1
那么5x^2+10x-3
=5(-2x+1)+10x-3
=-10x+5+10x-3
=2