find the expression as the cosine of an angle>> cos (pi/5)cos pi/3-sin(pi/5)sin pi/3

Hello!

It is a relatively simple task. The only formula we need to solve this is the formula of cosine of a sum of two angles:

This formula is true for any real numbers We shall use it in the reverse direction:

Hello!

It is a relatively simple task. The only formula we need to solve this is the formula of cosine of a sum of two angles:

This formula is true for any real numbers We shall use it in the reverse direction:

In our case we have (or vice versa). From the above formula we obtain

which is clearly equal to It is the answer.