Monday

October 20, 2014

October 20, 2014

Posted by **Michael** on Sunday, March 21, 2010 at 9:14pm.

- Trigonometric -
**Reiny**, Sunday, March 21, 2010 at 11:02pmsometimes it is easier to think in degrees, and then switch back

7π/12 = 105 degrees and 105 = 60+45

both angles that we know

cos 105

= cos(60+45)

= cos60cos45 - sin60sin45

= (1/2)(√2/2) - (√3/2)(√2/2)

= (√2 - √6)/4

so cos7π/12 = (√2-√6)/4

**Answer this Question**

**Related Questions**

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

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

trig - using the trigonometric identities find the exact (radical form) value of...

Trig - How do you express sin4x as a trigonometric funcition of x using the ...

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

pre-calculus - use a sum or difference formula to find the exact of the ...

Calculus - find the exact value of sin 11pi/12 using the sum or difference ...

Math- Trig - 1. Determine the exact value of cos^-1 (pi/2). Give number and ...

Trigonometry - I don't understand how I'm supposed set the problem up or what ...

Algebra 2 Honors - Find the exact value by using an appropriate sum or ...