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Core 3: differentiating trigonometric functions help please :)

The question is
show that y=sinx +2cos x has a stationary point when tanx=1/2
I have no idea what to do with this :frown: I've tried differentiating it but that got me nowhere as I got
dy/dx=cosx-2sinx and don't know what to do with this :frown:
pleas help! rep given :biggrin:
mammamia:0
The question is
show that y=sinx +2cos x has a stationary point when tanx=1/2
I have no idea what to do with this :frown: I've tried differentiating it but that got me nowhere as I got
dy/dx=cosx-2sinx and don't know what to do with this :frown:
pleas help! rep given :biggrin:


You're nearly there!! At a stationary point, dy/dx = 0 so cosx - 2sinx = 0 - then it's just re-arranging!!
Yah, dy/dx=0 so cosx - 2sisx = 0
Divide all terms by cosx:
1 - 2tanx = 0
tanx = 1/2
Reply 3
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-beads-
Carter_C
Yah, dy/dx=0 so cosx - 2sisx = 0
Divide all terms by cosx:
1 - 2tanx = 0
tanx = 1/2


don't post full solutions!

But OP, do you now understand, that you have the solution?

Good luck with future questions, just remember, at a stationary point, dy/dx = 0 and follow a question through, don't be shy. :p:

:smile:

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