Double Angle Formulae Problems Watch

mfred123
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#1
Report Thread starter 7 years ago
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Hi All,

I was going through some IB SL past papers and keep getting stuck on questions involving double angle formulae. I just have no idea where to start. Could anyone be so kind as to explain the following two questions to me please?

Much appreciated!



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vc94
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13.
30sin(3x)cos(3x) = 15*2sin(3x)cos(3x)

Can you apply the double angle identity sin2A=2sinAcosA ?
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baffled_mathman
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6.

It would help if it were all in terms of cos x and cos^2 x. So how can we express cos 2x in terms of cos^2 x?
And how can we express sin^2 x in terms of cos^2 x?
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vc94
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6.
Use cos2A=2cos^2(A) -1 and also express the sin^2(x) in terms of cos^2(x). This will simplify the equation to a quadratic in cosx.
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