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# Using Sin/Cos/Tan graphs for trigonemetry watch

1. Hi,

Currently I have used the CAST quadrant method in C2 to work out angle within limits like:

cos2x = -0.9

0 < x < 180

I know that I should get

2x = 154.15

but what do I do after this and how do I use the sin graph to work out the angles?

Thanks
2. (Original post by Sameer599)
Hi,

Currently I have used the CAST quadrant method in C2 to work out angle within limits like:

cos2x = -0.9

0 < x < 180

I know that I should get

2x = 154.15

but what do I do after this and how do I use the sin graph to work out the angles?

Thanks
You don't; you use the cos graph.

Pick a value on the y-axis of the cos(2x) graph. Now, go along to see how many times you hit the graph.

You can effectively read off the solutions using the symmetry of the graph.
3. (Original post by Sameer599)
Hi,

Currently I have used the CAST quadrant method in C2 to work out angle within limits like:

cos2x = -0.9

0 < x < 180

I know that I should get

2x = 154.15

but what do I do after this and how do I use the sin graph to work out the angles?

Thanks
Well, wether you use CAST or the Cos graph you find other values that also have cos(value) = -0.9

If using the graph you simply use the symmetry
4. Yep sorry, my mistake.

So this is the cos graph, could you direct it from there please? I also know the limit should be 360 since you times 180 by 2.
5. (Original post by Sameer599)
Yep sorry, my mistake.

So this is the cos graph, could you direct it from there please? I also know the limit should be 360 since you times 180 by 2.
Draw a line across at approx -0.9

use symmetry

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