Question
Use sum-to-product formulas to find the solutions of the equation.$$\cos 3 x+\cos 5 x=\cos x$$
Step 1
The sum-to-product formula for cosine is given by: $$\cos a + \cos b = 2 \cos \left(\frac{a+b}{2}\right) \cos \left(\frac{a-b}{2}\right)$$ Applying this to our equation, we get: $$\cos 3x + \cos 5x = 2 \cos 4x \cos x = \cos x$$ Show more…
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