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# tan x in terms of tan 2x watch

1. can I have tan x in terms of tan 2x ?
If yes
write it
can I have tan x in terms of tan 2x ?
If yes
write it
Take the identity for tan(2x) in terms of tan(x), reareange it into a quadratic for tan(x), solve it.
3. T = 2t/{ 1- t2 }

make t the subject

*T = tan2x

t = tanx
4. (Original post by RDKGames)
Take the identity for tan(2x) in terms of tan(x), reareange it into a quadratic for tan(x), solve it.

I could not
can you do it for me plz
5. (Original post by the bear)
T = 2t/{ 1- t2 }

make t the subject

*T = tan2x

t = tanx
how?
how?
rearrange it to get a quadratic equation with t as the variable, as RDK suggested above.
how?
(Original post by the bear)
rearrange it to get a quadratic equation with t as the variable, as RDK suggested above.

I could not rearrange themcan you help me?
I could not rearrange themcan you help me?

T = 2t/{ 1- t2 }

T{ 1 - t2 } = 2t

T - t2T = 2t

- t2T = 2t - T

t2T =- 2t +T

t2T + 2t - T =0

now use the quadratic formula with a = T, b = 2, c = -T
9. (Original post by the bear)
T = 2t/{ 1- t2 }

T{ 1 - t2 } = 2t

T - t2T = 2t

- t2T = 2t - T

t2T =- 2t +T

t2T + 2t - T =0

now use the quadratic formula with a = T, b = 2, c = -T
Thank you
10. (Original post by the bear)
T = 2t/{ 1- t2 }

T{ 1 - t2 } = 2t

T - t2T = 2t

- t2T = 2t - T

t2T =- 2t +T

t2T + 2t - T =0

now use the quadratic formula with a = T, b = 2, c = -T
There are two solutions to the equation.
Can I exclude one of the solutions?
There are two solutions to the equation.
Can I exclude one of the solutions?
yes... for instance if T = tan 60°

tan 30° = t

===> tan230° + 2tan30° - tan60° = 0

this must only give a single, positive, value for tan30° so we can discard the negative answer.

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