sine, what is it, how do I find it, and what do I do with it

G

guitarplay

New member
Joined
Feb 21, 2006
Messages
3
hey, Im new and probably wont be asking a lot of questions. I dont know if im in the right place, but I belive i need some help with trigonometry, but it might be something else.

I have a point, and I can determine that it is going to translate along a certain slope. I can get the slope, and the distance, but what im ineterested in, is fiding the sine value and converting to degrees.

It will start facing down (this is in flash), because there is gravity, so it will be facing down. Now, when i do something to change the direction, I can determine how it will be mooving before it has moved, and what I want to do, Is right before it actualy makes the move in the direction, I want to have the figure facing it.

Easily, I can change the rotation in degrees, so if it is headed up, I can change it to 180 and when to right, I can change to 90, and when to left, I can change to 270. What I need is to be able to fill in the rest. I have a sine table to convert sine to degrees 0-89, and I can determine the rest of the 271 using simple tests and adding either 90, 180, or 270 degrees to the number.

So if you could tell me how to find the sine (what it exactly is in the first place) and how do I use it, that would be awsome. I know it has something to do with the side opposite some angle and next to the cosin thingy but im only in geometry as a freshman so Im sort of lost.
 
So when it is moving down the angle is 0°?
The sine is the ratio of distance it moves left or right to the actual distance it has moved.

So if it moves sqrt(3) down and 1 right it has moved sqrt(1+3)=2.
sin<sup>-1</sup>(1/2) = 30°

If it moves sqrt(3) up and 1 right it has moved sqrt(1+3)=2 and your table will still say 30° but you have to subtract that from 180° for the correct answer of 150°
 
ok, again I looked at that page, and others like it and im still in geometry so. .

Can anyone explain in a simple way, how, If i have a slope which I can use to create a right triangle, how I get a number of degrees the angle is that is formed from the slope and the bottom of the right traingle. Il make an example.

Code: 
 /\
 |
 |
 |                 (4,6)
 |                  /|
 |                /  |
 |              /    |
 |            /      |
 |   |2,3|  /        |
 |        /          | 
 |      /            |
 |    /              |
 |  /                |
 |/*_ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _\
(0,0)              (4,0)                 /
the |2,3| is the slope.

* this is the angle I need to get. I can set up the grid any way, because i can get the x and y coordinates of the object, and use them as if they are (0,0) and then I can get the slope, and from it, eveything else.

If i knew the angle, I could just make it so that 0 degrees is facing from (0,0) down twards (0, whatever) so for this, I could tell if it was moving in this direction, get the slope and just say the angle is (* + 90) (or ((90-*) + 180), depending on which way it counts degrees.
 
guitarplay said:
ok, again I looked at that page, and others like it and im still in geometry so. .

Can anyone explain in a simple way, how, If i have a slope which I can use to create a right triangle, how I get a number of degrees the angle is that is formed from the slope and the bottom of the right traingle. Il make an example.

Code: 
 /\
 |
 |
 |                 (4,6)
 |                  /|
 |                /  |
 |              /    |
 |            /      |
 |   |2,3|  /        |
 |        /          | 
 |      /            |
 |    /              |
 |  /                |
 |/*_ _ _ _ _ _ _ _ _|_ _ _ _ _ _ _ _ _ _\
(0,0)              (4,0)                 /
the |2,3| is the slope.

* this is the angle I need to get. I can set up the grid any way, because i can get the x and y coordinates of the object, and use them as if they are (0,0) and then I can get the slope, and from it, eveything else.

If i knew the angle, I could just make it so that 0 degrees is facing from (0,0) down twards (0, whatever) so for this, I could tell if it was moving in this direction, get the slope and just say the angle is (* + 90) (or ((90-*) + 180), depending on which way it counts degrees.
Click to expand...

This triangle is drawn in standard position, in the first quadrant (to the right of the y-axis and above the x-axis). Sine* =
measure of opposite side
-----------------------------
meas. of hypotenuse

where the hypotenuse is the line you have called the slope (the line from (0,0) to (4, 6).

Sine is the ratio of the specified sides and for a particular angle, the ratio is fixed, no matter what size the actual figure. That is, sine 30 = 1/2.

Here, if you knew that the measure of the hypotenuse = 12 and you knew that the side opposite your angle * = 6, then you would know that sine* = 6/12 = 1/2, and therefore * = 30º.

I hope that gives you some of the information you're seeking.
 
gotcha, so I need to use the distance formula of

square root of|(x1-x2)squared + (y1-y2)squared|

that is the distance formula right?? so it would be

|(0-4)squared + (0-6)squared|
|16+36|
|52|
7.2111. . . (7.2)

then 6/7.2 = 0.83 repeting

so the angle is. . . 56 degrees


Thats how you do it. . . thats good.




Now, what would realy make my life simple, Is if there was a formula to figure out the angle from sine value, because I dont realy like the ideo of typing in 90 different values for sine and angles and all that.
 
guitarplay said:
gotcha, so I need to use the distance formula of

square root of|(x1-x2)squared + (y1-y2)squared|

that is the distance formula right?? so it would be

|(0-4)squared + (0-6)squared|
|16+36|
|52|
7.2111. . . (7.2)

then 6/7.2 = 0.83 repeting

so the angle is. . . 56 degrees


Thats how you do it. . . thats good.




Now, what would realy make my life simple, Is if there was a formula to figure out the angle from sine value, because I dont realy like the ideo of typing in 90 different values for sine and angles and all that.
Click to expand...

The angle whose sine is 1/2 is called the arcsine (for a calculator, INV sine) and is indicated as arcsine ½ or sine^-¹ ½.
sine^-¹ 1/2 = 30º

Calculators have the entire table of values programmed in them. If you knew that the sine was .7070 but wanted to know the angle, you could use your calculator:

Enter .7070 INV sin in that order and the calculator will tell you the angle measure (be sure your calculator is set for degrees if you want an answer in degrees).
 
You must log in or register to reply here.
Top