A line is tangent to the circle (x+4)2+(y+9)2=10\displaystyle {\left({x}+{4}\right)}^{{2}}+{\left({y}+{9}\right)}^{{2}}={10} at the point (1,8)\displaystyle {\left(-{1},-{8}\right)}. Find the equation of the line in slope-intercept form. 

 y=\displaystyle {y}=