trig
posted by carolyn .
sin t /1cos t  1+ cos t/sin t= 0

sin t /(1cos t)  (1+cos t)/sin t
sin t (1+cos t)/((1cos t)(1+cos t))  (1+cos t)/sin t
sin t (1+cos t)/(1cos^2 t)  (1+cos t)/sin t
sin t (1+cos t)/sin^2 t  sin t (1+cos t)/sin^2 t
0