Nathan's Blog

In this blog, I will explain chapter 10 section 1. This is the first section of the second nine weeks, and I think everyone, including me, got the hang of this on the first day.

Rule number one(worst rule ever): NO CALCULATOR!!!!

Another good thing to know, is the Trig Chart. This will save you.

Here are the formulas you will need to know:

(cos(alpha)+-(beta)=cos(alpha)cos(beta)-+sin(alpha)sin(beta)

sin(alpha)+-(beta)=sin(alpha)cos(beta)+-cos(alpha)sin(beta)
This may seem complicated, but it really isn't.

Ex. Find the exact value of sin15

To solve this, you must find two trig chart angles that add or subtract to give you 15.
alpha=45
beta=30
45-30=15

Now, you just plug it into the sin formula.

sin(45-30)=sin45cos30-cos45sin30
=(√2/2)(√3/2)-(√2/2)(1/2)
=√6/2-√2/4=√6-√2/4

sin15=√6-√2/4

Ex.2 Find the exact value of: cos(75)

alpha=45
beta=30

cos(45+30)=cos(45)cos(30)-sin(45)sin(30)
=(√2/2)(√3/2)-(√2/2)(1/2)
=√6/2-√2/4

cos75=√6-√2/4
It's the same answer as the first one if you didn't catch on.

See how easy this section is. Like all of them, this chapter is only going to get harder.