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Trig - HSN forum

# Trig

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### #1kimmy72889

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Posted 05 April 2005 - 10:26 AM

has anyone done this one?

im getting an answer but its the wrong one

### #2werlop

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Posted 05 April 2005 - 10:32 AM

Is that supposed to be cos (2x) or cos ^2 (x)

I'm assuming you mean the former, yes?

Are losing theirs and blaming it on you,
If you can trust yourself when all men doubt you
But make allowance for their doubting too,
If you can wait and not be tired by waiting,
Or being lied about, don't deal in lies,
Or being hated, don't give way to hating,
And yet don't look too good, nor talk too wise:
Yours is the Earth and everything that's in it,
And--which is more--you'll be a Man, my son!

### #3kimmy72889

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Posted 05 April 2005 - 10:54 AM

yeah 3cos(2x)

### #4Dave

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Posted 05 April 2005 - 11:10 AM

3cos(2x)+cosx = -1

sub in expansion of cos(2x) = 2cos2x-1

3(2cos2x-1) + cos x = -1

6 cos2x + cos x - 3 = -1

6 cos2x + cos x - 2 = 0

factorise

(3cosx + 2)(2cosx - 1) = 0

3cos x + 2 = 0 2cosx - 1=0

x = 131.8 and 228.2 x = 60, 300

If i am not here i am somewhere else

### #5kimmy72889

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Posted 05 April 2005 - 11:13 AM

thank you

### #6Dave

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Posted 05 April 2005 - 11:14 AM

so is that right then!

If i am not here i am somewhere else

### #7kimmy72889

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Posted 05 April 2005 - 11:15 AM

yes perfect (as usual )

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