Wednesday

October 1, 2014

October 1, 2014

Posted by **Omar** on Tuesday, October 11, 2011 at 9:19pm.

- trig -
**Reiny**, Tuesday, October 11, 2011 at 10:42pmuse

cos 2A = cos^2A - sin^2A

cos2A = cos^2A - (1 - cos^2A) = 2cos^2A - 1

cos 45° = 2cos^2 22.5° - 1

√2/2 + 1 = 2cos^2 22.5

√2/4 + 1/2 = cos^2 22.5°

cos 22.5° = √[ (√2 + 2)/4 ]

= √(√2 + 2) /2

**Answer this Question**

**Related Questions**

Trigonometry - use the appropriate trig identity (sum and difference, half angle...

trig - using the fact that 5pi/8=1/2(5pi/8) and the half angle identity for cos ...

trig - use a half-angle identity to find the exact value of tan 105 degrees.

Trig - Find the exact value of tan 5pi/12 using the half-angle identity.

MATH - 1.)Find the exact solution algebriacally, if possible: (PLEASE SHOW ALL ...

trig - find the exact value by using the appropriate half-angle identity: sin(...

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

Algebra II - Multiple Choice (theta) means the symbol 0 with the dash in it. 1.)...

Algebra II - 1) Find the exact value of cos 105 degrees by using a half-angle ...

Trig - Use a half-angle identity to find the exact value for sec(x/2) if sinx...