The expression is:
cos (π / 5) cos (π/7) + sin (π/5) sin(π/7)
This expression can be reduced into a trigonometric function with one angle if we make use of the trigonometric identities. The appropriate identity is:
cos (A - B) = cos A cos B + sin A sin B
If we let
A = π / 5
B = π / 7
Therefore,
cos (π / 5) cos (π/7) + sin (π/5) sin(π/7) = cos (π/5 - π/7) = cos (2π/35)
<em>The result is -13</em>
<h2>
Explanation:</h2><h2 />
Here we have the following addition problem:

So let's solve this step by step:
Step 1. Perform two plus two.

So:

Step 2. Perform the subtraction.
Since the sign (-) accompanies 17 which is greater than 4, then we perform the subtraction and add the sign (-) to the result. So:

<em>Finally, the result is -13</em>
<h2>Learn more:</h2>
Distributive property: brainly.com/question/10794694
#LearnWithBrainly
So you're suppose to isolate the variable by dividing each side by factors that don't contain the variable.
Which equals or at least.. Makes x = −
4
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I hope this helps, as always. I wish you the best of luck and have a nice day, friend..