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December 26th, 2013, 11:13 AM   #1
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Math problem

I have some problem solving this. I know I should use Euler's formula but I get stuck here.

How do I continue from here?

And this one.

Any idea how to solve this one?
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January 10th, 2014, 02:32 AM   #2
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As sin(3x) = 3sin(x) - 4sin(x), sin(x) = (-sin(3x) + 3sin(x))/4,
so sin(x)cos(3x) = (-2sin(3x)cos(3x) + 6sin(x)cos(3x))/8 = (-sin(6x) + 3sin(4x) - 3sin(2x))/8.

The second problem is mistyped.
Assuming it should be
one gets

Hence x = ? ?/6 + 2k?, where k is an integer.
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