## Wednesday, March 19, 2008

### Sum and Difference Identities

Hey Class, it's me again scribing for you. In this particular class, we took a kinesthetic approach in learning about identities. We were given 4 formulas, although Mr. K prefers not to use formulas and would rather have us understand where those formulas are derived from instead. The formulas seemed like quite a task to memorize so... we had a little help. From the greatest mathematical dance of all time:
THE SINE DANCE
.

Sin(α + β) = SinαCosβ + CosαSinβ
Sin(α - β) = SinαCosβ - CosαSinβ
Cos(α + β) =
CosαCosβ - SinαSinβ
Cos(
α - β) = CosαCosβ + SinαSinβ

This dance contains three easy steps which are called: SINE, COSINE AND BUST A MOVE! The order of which the steps are performed are located in the formulas shown above. In the first step sine, which is used to represent all the sine functions, we stick our arms out with one behind our back and bend them so that it forms the letter "s". The next step cosine, is even more simple than the first and is used to represent all the cosine. All you have to do is make the letter "c" with your arms. The final step is used to represent the sign change that cosine makes. To perform this step, you rotate your body 180 degrees and then hold your arms in front of your chest and make the letter "x". Once you have those down, feel free to use it as often as you like to aid you prove the sum and difference identities because that's what we did next except without the dancing.

Well, my scribe post is over now so that means I get to choose the next scribe. The next scribe is Paul. This begins cycle three.

By the way, I found about that writing your name in red ink thing. It turns that that superstition is Japanese. Still not sure if bad luck comes to the writer or the person who's name is written.

#### 1 comment:

m@rk said...

Anhthi,

Good scribe post. This scribe post sort of reminded me of the JABBAWOCKEEZ because of the way that you use kinesthetics to learn the sum and difference identities. Next year, if you take Calculus with Mr. K you guys will not just dance but also sing. Also, about that superstition about writing your name in red ink, my friend said that it doesn't mean anything important. Keep up the good work!

-m@rk