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# Trigonometric identities (C2) watch

1. Help would be much appreciated please I've been able to do most of the others of this nature, but for some reason I can't do this one!

3tanx = cosx

This is my working so far, sure I must have gone wrong somewhere though.
3tan^2(x) = tanxcosx
3tan^2x - tanxcosx = 0
tanx(3tanx - cosx) = 0
tanx = 0
or 3tanx = cosx
3sinx = cos^2x
3sinx = 1 - sin^2x
sin^2x + 3sinx -1 = 0 - but I don't think this will factorise?

Thanks
2. (Original post by iridescence.)
Help would be much appreciated please I've been able to do most of the others of this nature, but for some reason I can't do this one!

3tanx = cosx

This is my working so far, sure I must have gone wrong somewhere though.
3tan^2(x) = tanxcosx
3tan^2x - tanxcosx = 0
tanx(3tanx - cosx) = 0
tanx = 0
The working up to here is not only redundant, it's introduced an additional solution tanx=0, which doesn't satisfy the original equation.

or 3tanx = cosx
This is what you were given to start with

3sinx = cos^2x
3sinx = 1 - sin^2x
sin^2x + 3sinx -1 = 0 - but I don't think this will factorise?

Thanks
Your working for this last bit is fine, and as you notice it doesn't factorise, so you'll need to use the quadratic formula on this bit.
3. (Original post by ghostwalker)
The working up to here is not only redundant, it's introduced an additional solution tanx=0, which doesn't satisfy the original equation.

This is what you were given to start with

Your working for this last bit is fine, and as you notice it doesn't factorise, so you'll need to use the quadratic formula on this bit.
Thank you so much, makes so much more sense now!
4. (Original post by iridescence.)
Thank you so much, makes so much more sense now!

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