Friday

February 27, 2015

February 27, 2015

Posted by **lina** on Tuesday, April 3, 2012 at 4:06pm.

cos(-13pi/12)

- pre-calculus -
**Steve**, Tuesday, April 3, 2012 at 5:31pmcos(-13pi/12)

= cos(-13pi/12 + 24pi/12)

= cos(11pi/12)

= -cos(pi - 11pi/12)

= -cos(pi/12)

now, cos(x/2) = √((1+cos(x))/2)

-cos(pi/12) = -√((1+cos(pi/6))/2)

= -√((1+√3/2)/2)

= -√(2 + √3/4)

= -1/2 √(2+√3)

or

-1/2√2 (1+√3)

**Answer this Question**

**Related Questions**

Homework Help Calculus - Find the linear approximation L(x)of the function f(x)=...

TRIG/ALGEBRA - 1) Find the exact value. Use a sum or difference identity. tan (-...

Math - Use the sum or difference identities to find the exact value of each ...

Math - Given that cos 13pi/18=sin y, first express 13pi/18 as a sum of pi/2 and ...

Trigonometry - If cos(a)=1/2 and sin(b)=2/3, find sin(a+b), if 1) Both angles ...

Precalculus/Trig 6 - Find the exact value of the following trigonometric ...

trig - Cos(-11/12) use the sum or difference formula to find the exact number

trig - use sum or difference identities to find the exact value of the ...

trig - determine an exact expression for the trigonometric function sin(13pi/12...

math - Use the appropriate sum/difference formula to find the exact value of cos...