Answer:
see explanation
Step-by-step explanation:
Using the trigonometric identity
tanx = [tex]\frac{1}{cotx}[/tex]
Consider the left side
[tex]\frac{cotA-1}{cotA+1}[/tex] ← divide terms on numerator/denominator by cotA
= [tex]\frac{\frac{cotA}{cotA}-\frac{1}{cotA} }{\frac{cotA}{cotA}+\frac{1}{cotA} }[/tex]
= [tex]\frac{1-tanA}{1+tanA}[/tex]
= right side , thus proven
