# Cos20cos30 + sin20sin30 ?

##### 1 Answer

Feb 28, 2018

See explanation...

#### Explanation:

Alright, this is one of the 3 massive fundamental rules of trigonometry. There three rules are:

1)

2)

3)

Rule three here is interesting because this can also be written as

This is true because

Alright, now that we understand that, lets plug in you number to the formula. In this case,

So the final answer is

Hope this helped!

~Chandler Dowd