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# Trig help watch

1. I'm doing a question that wants me to calculate the exact value of cos(210) - I understand most of it but there's a step that's really messing me up.

They used the CAST diagram to show cos(210) = -cos(30) and I don't understand the cast diagram as I use the graphs, is it possible to show on the cos graph itself as I'm really struggling??
2. If you draw out y=cos(x) and y=-cos(x) it makes it easier to see
3. (Original post by jazzyp234)
If you draw out y=cos(x) and y=-cos(x) it makes it easier to see
Thank you!! How would you be able to quickly work that out if it was asked in an exam, that's where I'm stuck. Is it just something I should know?
4. If I'm stuck I just draw out the info they give me which normally helps me to see the solution. I find CAST diagrams the quickest way for simpler problems so they are useful to at least know and can be used for lots of different problems.

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Updated: October 26, 2015
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