SOLUTION: am stuck with this question on proving in geometry. Given a triangle ABC prove that {{{cot(C) = expr(a/c)cosec(B)- cot(B)}}} the substitution has been slightly tricky

Next draw an altitude (perpendicular) from A to BC, 
and label it h.

That green altitude divides the base BC of length "a" 
into two parts, we'll let "x" represent the right part 
of "a", and the left part will be "a-x"


 
 

Using the right triangle on the right:



Using the right triangle on the left:





Substituting into 





Cancel the c's in the first term on the right:





The fractions on the right have a common denominator so
we can combine the numerators:







Edwin