We know that:
tantheta=sintheta/costheta
and
cottheta=1/tantheta
So we can plug in our values:
color(white)=cot(theta)
=1/tan(theta)
=1/(sintheta/costheta)
=1/(sintheta/costheta)color(blue)(*costheta/costheta)
=1/(sintheta/color(red)cancelcolor(black)costheta)color(blue)(*costheta/color(red)cancelcolor(blue)costheta)
=1/sinthetacolor(blue)(*costheta)
=costheta/sintheta
Now plug in our values:
=(-12/13)/(-5/13)
=(-12/13)/(-5/13)color(blue)(*13/13)
=(-12/color(red)cancelcolor(black)13)/(-5/color(red)cancelcolor(black)13)color(blue)(*color(red)cancelcolor(blue)13/color(red)cancelcolor(blue)13)
=(-12)/(-5)color(blue)(*1/1)
=(-12)/(-5)
=(color(red)cancelcolor(black)-12)/(color(red)cancelcolor(black)-5)
=12/5
That's the solution. Hope this helped!