Saturday

December 20, 2014

December 20, 2014

Posted by **kk** on Monday, April 2, 2012 at 12:47pm.

- trig -
**Steve**, Monday, April 2, 2012 at 1:20pmcos^2 θ/2 = (1 + cosθ)/2

cos^2 22.5° = (1 + cos 45°)/2

= (1 + √2/2)/2

= (2 + √2)/4

- trig -
**Steve**, Monday, April 2, 2012 at 1:37pmhmmph

It would help to notice that

2cos^2 θ - 1 = cos 2θ

so what you have is just cos 45° = 1/√2

note that 2(2+√2)/4 - 1 = 1+√2/2-1 = √2/2 = 1/√2

**Answer this Question**

**Related Questions**

trig - Find minimum value of 2cos x + 2cos y

trig - Find minimum value of 2cos x + 2cos y

trig - Find minimum value of 2cos x + 2cos y

Trig - If cosx = 10/19 an pi < x < 2pi, find the exact value of cos x/2 ...

trig - find the exact solutions (¦È in degrees) sin^2¦È+2cos¦È=-2 range= 0¡Ü¦È&...

trig/pre -calc - hello, i don't quite understand how to do this type of problem...

trig - how can i find all the exact solutions to the equation : 2cos^2x + 3sinx...

pre-calc - find the exact value of the given expression. Thank you! tan(1/2cos^-...

mathematics - give that sin( A + B )= 2cos(A - B ) and tan A = 1/3,Find the ...

trig - findall exact solutions ( in terms of radians) to the equation 2cos(40)-...