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Trigonometry

Could someone help with the following question?
Solve thefollowing in the interval -180° to 180°.
sinx ( cosx plus cosecx ) = 2cos^2 x

You don't have to give the solutions but just simplify the equation for me. I got as far as -cos^2 x plus sinxcosx plus sin^2 x. I just want to eliminate either cos or sin from the equation
(edited 4 years ago)
Original post by SeverusESnape
Could someone help with the following question?
Solve thefollowing in the interval -180° to 180°.
sinx ( cosx + cosecx ) = 2cos^2 x

You don't have to give the solutions but just simplify the equation for me. I got as far as cos^2 x + sinxcosx - sin^2 x. I just want to eliminate either cos or sin from the equation


Could you post your working so far?
once you have expanded the brackets you should think about how your terms relate to sin2x and cos2x :h:
Original post by Muttley79
Could you post your working so far?

Doesn't really matter. The equation I got to so far has been given up there ^
@RDKGames help...?
(edited 4 years ago)
Original post by SeverusESnape
Could someone help with the following question?
Solve thefollowing in the interval -180° to 180°.
sinx ( cosx + cosecx ) = 2cos^2 x

You don't have to give the solutions but just simplify the equation for me. I got as far as cos^2 x + sinxcosx - sin^2 x. I just want to eliminate either cos or sin from the equation


Should have cos2x+sinxcosx+sin2x=0-\cos^2 x + \sin x \cos x + \sin^2 x = 0 instead.

Now just apply the double angle formulae?
Original post by RDKGames
Should have cos2x+sinxcosx+sin2x=0-\cos^2 x + \sin x \cos x + \sin^2 x = 0 instead.

Now just apply the double angle formulae?


Yeah sorry that's what I got. But how do i proceed further? Which double angle formula?
Original post by SeverusESnape
Yeah sorry that's what I got. But how do i proceed further? Which double angle formula?


sin(2x) can be used on the middle term.

cos(2x) can be used on the two leftover terms.

Do you see it??
Original post by RDKGames
sin(2x) can be used on the middle term.

cos(2x) can be used on the two leftover terms.

Do you see it??


Yeah I totally do but I don't see how that would help me get my solutions for x..?
Original post by SeverusESnape
Yeah I totally do but I don't see how that would help me get my solutions for x..?


The point is that you use these to get an eqn in tan(2x)
Original post by RDKGames
The point is that you use these to get an eqn in tan(2x)


AHHH ok thanks a lot!!

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