Question

两条直线l1：y=kx+2k+1,l2;y=-1/2x+2的交点在直线x-y=0的上方,则k范围?

Answer 1

选C

y=kx+2k+1

y=-1/2x+2

联立解方程组

kx+2k+1=-1/2x+2

(k+1/2)x=1-2k

x=(1-2k)/(k+1/2)=(2-4k)/(2k+1)

代入y=-1/2x+2得

y=-1/2*(2-4k)/(2k+1)+2=(2k-1)/(2k+1)+2=(6k+1)/(2k+1)

在x-y=0的上方,则

x