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# Cosine equation help Watch

1. The question is
http://www.examsolutions.net/a-level...estions/q4.gif

I found out that one answer is 41.2 but I understand there are more. How do I find these? I remember used to doing this and using CAST if anyone know what that is?
2. I did 360-41.2 and got 318.8. That's not in the range. I dont get it?
3. (Original post by Year11guy)
The question is
http://www.examsolutions.net/a-level...estions/q4.gif

I found out that one answer is 41.2 but I understand there are more. How do I find these? I remember used to doing this and using CAST if anyone know what that is?
When you had 3x-10 = 113.6

You need to realise that (using CAST) angles with negative cosines are in the second and third quadrants

Find more angles that have a cosine of -0.4 and add 10, then divide by 3

4. (Original post by TenOfThem)
When you had 3x-10 = 113.6

You need to realise that (using CAST) angles with negative cosines are in the second and third quadrants

Find more angles that have a cosine of -0.4 and add 10, then divide by 3

I'm sorry but Im still not getting it. I have got 41.2 degrees. Using that, how do I find out the rest?
5. (Original post by Year11guy)
I'm sorry but Im still not getting it. I have got 41.2 degrees. Using that, how do I find out the rest?
You don't

As I said you find the rest by using the 113.6 in the CAST diagram
6. (Original post by TenOfThem)
You don't

As I said you find the rest by using the 113.6 in the CAST diagram
Ok I got 85.5 degrees and 41.2 degrees. 161.2 degrees is an answer but that requires me to do 360+113.578.. which isn't part of CAST?
7. (Original post by Year11guy)
Ok I got 85.5 degrees and 41.2 degrees. 161.2 degrees is an answer but that requires me to do 360+113.578.. which isn't part of CAST?
I do not know what you mean isn't part of CAST

360+113.6 puts you in the second quadrant again so it is fine
8. (Original post by TenOfThem)
I do not know what you mean isn't part of CAST

360+113.6 puts you in the second quadrant again so it is fine
C 360-theta
A theta
S 180-theta
T 10+theta

Where does 360+theta fit in?
9. (Original post by Year11guy)
C 360-theta
A theta
S 180-theta
T 180+theta

Where does 360+theta fit in?
You can do 360 plus all of those and 720 plus all of those and ... ... ...

There are infinite solutions

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