Posted by **Steve** on Wednesday, December 16, 2009 at 9:57pm.

Use a half-angle formula to find the exact value of cos 5ð/12

- trig -
**Reiny**, Wednesday, December 16, 2009 at 10:11pm
your symbol for pi did not come out, just type pi, that seems to be the simplest way.

A lot of students seem to find it easier to think in degrees,

5pi/12 = 75º

cos(5pi/12) radians

= cos 75º

= cos(45 + 30)

= cos45cos30 - sin45sin30

= (√2/2)(√3/2) - √2/2)(1/2)

= (√6 - √2)/4

## Answer This Question

## Related Questions

- trig - use a half angle formula to find the exact value of cos 75 degree
- Trig - If cosx = 10/19 an pi < x < 2pi, find the exact value of cos x/2 ...
- Trig - Use the half angle formula to find the exact value of tan 7 pie/8
- MATH - 1.)Find the exact solution algebriacally, if possible: (PLEASE SHOW ALL ...
- Mathmatics - a. Use the formulas for lowering powers to rewrite the expression ...
- Please help Math - a. Use the formulas for lowering powers to rewrite the ...
- trig - Find the exact value by using a half-angle identity. cos 22.5 degrees
- Trig - How do i find the exact value of sin 15 using the half angle formula
- Trigonometry - use the appropriate trig identity (sum and difference, half angle...
- Trig - Use the half-angle formulas to come up with an exact expression for each ...

More Related Questions