Question 870244
Start with substituting the definitions for cotangent in the left side member.

{{{(cos(x)+cos(x)/sin(x))/(sin(x)+1)}}}


{{{(cos(x)sin(x)/sin(x)+cos(x)/sin(x))/(sin(x)+1)}}}


{{{((cos(x)sin(x)+cos(x))/sin(x))/(sin(x)+1)}}}


{{{(cos(x)sin(x)+cos(x))/(sin(x)(sin(x)+1))}}}


{{{(cos(x)sin(x)+cos(x))/(sin(x)(sin(x)+1))}}}, 


{{{(cos(x)sin(x)+cos(x))/(sin(x)(sin(x)+1))}}}


{{{(cos(x)(sin(x)+1))/(sin(x)(sin(x)+1))}}}


{{{(cos(x)cross((sin(x)+1)))/(sin(x)cross((sin(x)+1)))}}}


and you see the definition again of cotangent?