If sin y = cos 3y, determine an exact value for angle y.
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justaguide
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We have to find y such that sin y = cos 3y.
We know that sin(y) = cos(pi/2-y),so we can convert the given equation to:
sin(y) = cos(pi/2-y) = cos(3y)
We now equate pi/2 - y and 3y
pi/2 - y = 3y
=> pi/2 = 3y + y
=> 4y = pi/2
=> y = pi/8
Therefore y = pi/8 + 2*n*pi
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