త్రికోణమితి తత్సమాలు భాగం -2
Translated from original video
Title - Trig identities part 2 (part 4 if you watch the proofs)
URL -https://www.khanacademy.org/math/trigonometry/less-basic-trigonometry/trig_iden_tutorial/v/trig-identities-part-2--parr-4-if-you-watch-the-proofs