Recall that tan(x) = sin(x)/cos(x) and cot(x) = 1/tan(x) = cos(x)/sin(x).
Step one: Express tan(x)+cot(x) as one fraction in terms of cos(x) and sin(x);
tan(x)+cot(x)=sin(x)/cos(x) + cos(x)/sin(x) = (sin^2(x)+cos^2(x))/(sin(x)cos(x)) = 1/(sin(x)cos(x))
Step two: Multiply the above with 1/csc(x) = 1/(1/sin(x)) = sin(x)
(tan(x)+cot(x)) * 1/csc(x) = 1/(sin(x)cos(x)) * sin(x) = 1/cos(x) = sec(x)