Question

Given that cos(30°) = cos(45°)cos(15°) + sin(45°)sin(15°), it follows that cos(30°) =

Answer 1

square root 3/2

Explanation:

on usatestprep and the unit circle

Answer 2

`cos(30\°) = cos(45\°-15\°)`

Explanation:

To solve this problem you must know the formula of subtraction of angles for the function cosx.

The formula is:

`cos(h-d) = cos(h)cos(d) + sin(h)sin(d)`

We can write 30° as: 45° - 15°

Then:

`cos(30\°) = cos(45\°-15\°)`

Using the formula for subtraction of angles we have:

`cos(45\°-15\°) = cos(45\°)cos(15\°) + sin(45\°)sin(15\°)`

Notice that we have achieved the expression shown in the statement

Finally:

`cos(30\°) = cos(45\°-15\°)`