Math 一問....

y=kx-7---------1
y=x^2-10x+9------------2
Sub. 1 into 2
x^2-(10+k)x+16=0
The equation has only one solution
delta=0
(10+k)^2-4(16)=0
k^2+20k+100-64=0
k^2+20k+36=0
(k+2)(k+18)=0
k=-2 or k=-18