Overkill method: consider the expansion of :
Expand the right hand side and compare the real parts:
Rewrite the sines in terms of cosines by using the angle sum identity.
Then using the other variant of the same identity,
so that .
Answer:
1, 3, 5, 7
Explanation:
You can use the identity ...
Then ...
So, {a, b, c, d} = {1, 3, 5, 7}.
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