# Thread: depressed by degrees problem

1. ## depressed by degrees problem

Hi, I am a complete green horn on trig and have bought a rather naff "Trigonometry for Dummies" book that is beyond me.

I do not accept I cannot learn it as this book is not written in a way I can understand so have ordered another title.

Anyway onto my problem!

The coordinate plain is on the iPhone which is 320 * 460

The circle centre (is this the origin) is 160, 230

I use these equations to get my distance from centre and the degrees that this distance represents around the inside of the circle.

kSlideCentreX = 160 and kSlideCentreY = 230

Code:
distanceFromCentre = sqrt(((currentPosition.x - kSlideCentreX ) * (currentPosition.x - kSlideCentreX)) - ((currentPosition.y - kSlideCentreY) * ( currentPosition.y - kSlideCentreY)));
this is how I get the slope

Code:
slope = (kSlideCentreY - currentPosition.y) / (kSlideCentreX - currentPosition.x);

Code:
atan(slope)

gives me the degrees ( but not fixed yet )

Code:
atan(slope) / kRadiansPerDegree
this is supposed to fix them to real degrees?

Code:
90 - ( atan(slope) / kRadiansPerDegree)
my problem is that any coords on the right of the circle run from 180 degrees at the top (12) to 0 at the bottom (6), and on the left side from 180 at the bottom (6) to 0 at the top (12).

I can understand and learn things as long as they are done so in a fashion my brain can grasp

I am searching and searching but coming up blank probably due to not asking the right question or how to phrase it.

I would be very grateful if someone could point me in the right direction or if feeling very friendly and helpful tutor me through this problem so I can learn from it and expand?

in hope......

Thanks

2. I am not sure what you're asking for. What is it you want to understand?.

How to convert from radians to degrees?.

3. Hi, well starting from 12 to 3 I would expect to see 0 to 90 then from 3 to 6 90 to 180 from 6 to 9 180 to 270 and finally from 9 to 12 270 to 360.

But I get 180 to 90 to 0 to 90 to 180?

I don't understand why this is so ?

Tomorrow I am going to plot a circle on graph paper and draw a triangle in it to see if I can visualize the calculation of distance and subsequent angle to determine the degrees, but am struggling to understand.

Have spent a lot of time tonight trying to find a downloadable trig course for beginners!

4. In most applications the origin is the positive x-axis and travels counterclockwise. Therefore, as you have it in terms of a clock face.
0 is at 3, 90 is at 12, 180 is at 9 and 270 is at 6. Then it goes around and 360 is at 3 again.

The first quadrant is 0 to 90, second quadrant is 90 to 180, third quadrant is 180 to 270, fourth quadrant is 270 to 360(or 0).

To find angles, use $\displaystyle x=rcos{\theta}$ to find the x-coordinate

$\displaystyle y=rsin{\theta}$ to find the y-coordinate.

$\displaystyle r=\sqrt{x^{2}+y^{2}}$, Pythagorean theorem.

For instance, x=1 and y=1. $\displaystyle r=\sqrt{1^{2}+1^{2}}=\sqrt{2}$

That is the length of the hypoteneuse of the triangle formed.

Now, that is 45 degrees or $\displaystyle \frac{\pi}{4}$ radians.

$\displaystyle x=\sqrt{2}sin(\frac{\pi}{4})=1, \;\ \sqrt{2}cos(\frac{\pi}{4})=1$

See?. We got the coordinates (1,1).

This is a little different than the diagram because I used x and y of 1.

If we use r=1 as in the unit circle, then $\displaystyle x=1\cdot sin(\frac{\pi}{4})=\frac{\sqrt{2}}{2}$. Just as on the diagram.

Also, $\displaystyle y=1\cdot cos(\frac{\pi}{4})=\frac{\sqrt{2}}{2}$.

To convert from radians to degrees, multiply by $\displaystyle \frac{180}{\pi}$

To convert from degrees to radians, multiply by $\displaystyle \frac{\pi}{180}$

I have posted a diagram of the unit circle so you can see. Those Books for Dummies are not the best to learn from.

Does that help a wee bit?.

5. Yep it does help a see bit.

I understand the layout of the degrees and yep sure did drop the ball on that one LOL

I lost you on the finding the x a y equations but caught up again on the conversion to degrees from radians.

I would already have the x,y coords and would use the 3,4,5 rule to get the distance and use that for getting the degrees I think?

Do you know if the product at top of this page Trigonometry Solved would be of any help to me? I know jack about trig but must learn it fast for work!

Am trying to find. Course or book aimed at kids I suppose seeing as my knowledge of this is so poor!

Example I only found out tonight that sine = opposite / hyp!

See how little I know ?

6. Am just Reading an interesting web site on unit circle!

As I did not know what this was either

7. There are all sorts of things if you google.

We all have to start somewhere. I learned trig years back when I began surveying.

Here is a diagram of the triangle with its respective trig and what sides they represent.

Of course, if it is not a right triangle, then it gets more complicated.

Law of Sines, Law of Cosines and so forth come into play. Lots to learn.

8. Could someone confirm my thoughts that the example I have seen is wrong hence my confusion please?

OK...I am told of a right triangle with a 30 degree angle an opposite length of 4 and an unknown hypotenuse.

so to find the length hypotenuse, lets call it 'a' the following applies:

sin x = opposite / hypotenuse

sin 30 = 4 / a

a sin 30 = 4

a = 4 / sin 30

4 sin 30 = 8

Now I understand sin 30 = 0.5 so applying this to the above we get

0.5 = 4 / a ( a is 8 )

a 0.5 = 4 ( a is 8 )

a = 4 / 0.5 ( a is 8 )

4 0.5 = 8 ( no it does not? 4 0.5 = 2)

Have I missed something or is this last line an incorrect example?