Question

Probe that:
tan A - cotan A = -2 cotan 2A

Answer 1

I didn't understand your reply...

Answer 2

now we know that cos(2A) = cos^2(A) - sin^2(A)

Answer 3

and we know that sin(2A) = 2 sin A cos A , these are trig identities

Answer 4

tan A - cot A
= sin A / cos A - cos A / sin A
= ( sin^2 (A) - cos^2(A) ) / ( cos (A) sin(A) )
= - ( cos^2(A) - sin^2(A)) / (cos(A) sin (A))
= - ( cos(2A) ) / ( cos A sin A )
= - 2( cos (2A) ) / ( 2 cos A sin A )
= -2cos(2A) / ( sin (2A)
= -2 cot (2A)

Answer 5

OK, perl, now I understood your explanation.
Thank you very much! Bye!