(adsbygoogle = window.adsbygoogle || []).push({}); Please help me in these identities!!!!

I tried to solve these identities, but I don't think that these are identities exept the first,

1.) sin2α/1+cos2α=tanα

2.) 1-cosα/sinα=tanα/2

3.) tanα+ctanα=csecα

4.) 3cosα+cos3α/3sinα-sin3α=3/2

5.) sin18°+sin30°=sin54

At first i did this:

sin2α=2sinα*cosα

cos2α=cos^2α-sin^2α

1=cos^2α+sin^2α

sin2α/1+cos2α=2sinα*cosα/cos^2α+sin^2α+cos^2α-sin^2α=...=tanα

But I don't know what to do eith others i tried to substitute tanα=sinα/cosα and etc but no solve ,

please help me

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Please help me in these identities

**Physics Forums | Science Articles, Homework Help, Discussion**