Is cos(x+y)+cos(x-y)=2cos(x)cos(y) ?

The answer to whether cos(x+y)+cos(x-y)=2cos(x)cos(y) is True

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prove cos(x+y)+cos(x-y)=2cos(x)cos(y)

prove

cos (x + y) + cos (x - y) = 2 cos (x) cos (y)

True

Solution steps

cos (x + y) + cos (x - y) = 2 cos (x) cos (y)

Manipulating right side

2 cos (x) cos (y)

Rewrite using trig identities

2 cos (x) cos (y)

Use the Product to Sum identity:

cos (s) cos (t) = \frac{1}{2} (cos (s - t) + cos (s + t))

= 2 \cdot \frac{1}{2} (cos (x - y) + cos (x + y))

Simplify

2 \cdot \frac{1}{2} (cos (x - y) + cos (x + y)) : cos (x - y) + cos (x + y)

2 \cdot \frac{1}{2} (cos (x - y) + cos (x + y))

Multiply fractions:

a \cdot \frac{b}{c} = \frac{a \cdot b}{c}

= \frac{1 \cdot 2}{2} (cos (x - y) + cos (x + y))

Cancel the common factor:

2

= (cos (x - y) + cos (x + y)) \cdot 1

Refine

= cos (x - y) + cos (x + y)

= cos (x - y) + cos (x + y)

= cos (x - y) + cos (x + y)

= cos (x + y) + cos (x - y)

We showed that the two sides could take the same form

\Rightarrow True

1 - \frac{sin ^{2} ( x )}{1 + cos ( x )} = cos (x)

csc (x) - \frac{sin ( x )}{1 + cos ( x )} = cot (x)

sin (2 x) = \frac{2 tan ( x )}{1 + tan ^{2} ( x )}

(tan^{2} (x) + 1) (cos^{2} (x) - 1) = - tan^{2} (x)

sec^{2} (θ) (1 - sin^{2} (θ)) = 1

Is cos(x+y)+cos(x-y)=2cos(x)cos(y) ?
The answer to whether cos(x+y)+cos(x-y)=2cos(x)cos(y) is True