### -->|SCRIBE|<--

Well I'm today's scribe. The class today we learned how to guess what the answer will be if the question is the sin, cos of a length. For example:

sin30 = 1/2

sin150 = 1/2

sin210 = -1/2

sin330 = -1/2

How are these angles similar? They are all in 30degrees from 180 or 360.

You can figure this out if you know what the sin30 equals to. If sin150 is (+), why is the sin210 and sin330(-)?? Its negative because its in the 3rd and 4th quadrant. In sin, you'll know if its negative because anything pass 180degrees is negative. In other words, the degrees that are below the line of origin or under zero(0) in the y-axis is negative.

Another thing that Mr. K talk about is about cos. Cos is similar to the sin, in cos if the degree is in the 2nd or 3rd quadrant of the graph, it is negative. To make it easier if the angle that you're looking at is in the left side of the graph, negative side in the x-axis, the number is negative.

EXAMPLE:

cos60 = 1/2

cos120 =-1/2

cos240 =-1/2

cos300 =1/2

In this example all of the angles are 60degrees for the line of origin. Cos60 and cos300 are positive because they are in the 1st and 4th quadrant.

Mr. K also talked about inverses.

The inverse of:

-addition is subraction

-subtraction is addition

-multiplication is division

-division is multiply

This connects with the lesson because to get the length of the side you have to use sin or cos depending on what side you are calculating.

The inverse of:

-sin is ARCsin or sin-1

-cos is ARCcos or cos-1

The sin function is turns angle in to length and the ARCsin turns the length in to angle.

ANNOUNCEMENTS:

+Homework-Exercise 18 #1-3

Exercise 19 #11-20

+Sub tommorow - Mr Clark

+Possiblity of having a TEST ON TUESDAY NEXT WEEK OCT.25

Thats it folks! oohh yea... the scribe tommorow is----------------------------------------------------------------------->WENDY =P

## 2 Comments:

I DON"T WANTT TO BE THE SCRIBEE!!!!!!!!!!!!!!!!

This was a really good post Rus-L! I liked the way you emphasized how sine is related to a measurement along the y-axis and cosine to a measurement along the x-axis. By determining which quadrant an angle is in you can figure out if the sine or cosine is positive or negative.

Post a Comment

## Links to this post:

Create a Link

<< Home