Which of these is an identity?

Question

(A) $cotu=-sinu/cosu$
(B) $secu=-sin(1/u)$
(C) $cotu=1/tanu$
(D) $tan^2u+cot^2u=1$

1435 views around the world

You can reuse this answer
Creative Commons License

Answer 1 · 2017-01-19T14:34:49

(C) $cotu=1/tanu$ is the only identity

(A) $cotu=-sinu/cosu$ is not an identity as $cotu=cosu/sinu$ and not $-sinu/cosu$ .

(B) $sec u=-sin(1/u)$ too is not an identity as $secu=1/cosu$

(D) $tan^2u+cot^2u =1$ is not an identity as $tan^2u=1/cot^2u$

(C) $cotu=1/tanu$ is the only identity