Posted by Shasha on Tuesday, November 27, 2012 at 11:20pm.
Use some trig identities: tan(-x) = tan(x) csc(x) = 1/sin(x) tan(x) = sin(x)/cos(x) tan(-x)*csc(x) = tan(x)*(1/sin(x) = (sin(x)/cos(x))*(1/sin(x) = 1/cos(x) = sec(x)