Today, I’ll post something about trigonometric functions.

I found a useful posting about this but it’s in Korean so my work will merely translating them.

You can check it here if you can read Korean.

http://blog.naver.com/PostView.nhn?blogId=dalsapcho&logNo=20131746494

First, we will look at the form of ” asinx + bcosx”.

Note that the angles of sin and cos are same.

Think about a circle with 1 radius and its cross point between the vector (a,b)

Then cosΘ is the x-coordinate and sinΘ is the y-coordinate.

Hence, we can prove the formula like the above.

Addition, subtraction etc of trigonometric functions.

The proof is like below.

The reason of A is below

You can get other formula by using the first one.

e.g., but -B instead of B in the first formula.

So you need to remember only first one.

There are three 2 and 2 things to alternate (sin -> cos, + -> -)

I’ll upload about this if I need it.

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