PROVE THAT:

cos 20° - sin 20° = \sqrt{2}sin25°

See below.

Step-by-step explanation:

First, use the co-function identity:

We can turn the second term into cosine:

Substitute:

Now, use the sum to product formulas. We will use the following:

Substitute:

Use the even-odd identity:

Therefore:

Replace the second term with the original term:

Proof complete.

pay attention in your classes and concentrate the best thing you can do to raise your test scores is to pay attention when you're supposed to be learning the material: in class!

take good notes.

do your homework.

use mnemonics and other tricks.

do practice tests.

note: the best i know.

5+2x=a

asdasdsaadsaddsasds