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# Basic trig help please! watch

1. Given that sin(pi/3)=root3/2, and cos(pi/3)=1/2, use trig identities to determine the exact values of sin(2pi/3), cos(2pi/3), sin(5pi/6), and cos(5pi/6). WITHOUT USE OF CALCULATOR.

Thank you x
2. (Original post by Mulkeen)
Given that sin(pi/3)=root3/2, and cos(pi/3)=1/2, use trig identities to determine the exact values of sin(2pi/3), cos(2pi/3), sin(5pi/6), and cos(5pi/6). WITHOUT USE OF CALCULATOR.

Thank you x
This looks remarkably similar to a thread someone posted in the (University) Mathematics forum a couple of days ago

What have you tried so far?

3. To get started. You need to express the target angle in terms of the angles you have using the double angle formula and the formula for sum/difference of angles
4. Use your double angle identities, and as you move on to cos(5pi/6) and sin(5pi/6), you see that they logically follow.
Hint: cos(2pi/3 + pi/6)...

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Updated: November 11, 2015
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