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Stuck on c4 trig

Please help as I am stuck on a c4 trig question
I have to prove the formula and find all the ranges of the value for
Tan2x=3cotx within 0 and 180

And I don't even know how to prove that they are equal.
Any help would be really nice
Thanks x :smile:

Reply 1

the bear

look up identities for Tan2x and also for cotx.

Reply 2

the bear

here are some:

http://www.purplemath.com/modules/idents.htm

Reply 3

TenOfThem

Original post by AlexMasonx

Can you post the question

That is not an identity

The range suggests that this is an equation to be solved

Reply 4

LaytonProfessor

This is not an identity: this is an equation.

x = arctg(sqrt(3)/sqrt(5)) = 37.76°

You must know to do the equation:

tg(2x) = (2tgx)/(1-tg^2 x)

Good luck!

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Reply 5

WhiteGroupMaths

Tan2x=3cotx

(2 tanx)/[1-(tanx)^2] =3/ tanx

2(tanx)^2 = 3 [1-(tanx)^2]

Rearranging terms gives

5(tanx)^2 = 3 ====> (tanx)^2 =3/5 =0.6

You should be able to carry on from here without much trouble. Peace.