Posted by Anonymous on Sunday, October 17, 2010 at 2:05am.
Unless you have found sin15 or cos15 before, and it has become part of your trig repertoire , you will have to do it twice
since you must know that cos 30 = √3/2
cos 2A = 2cos^2 A - 1 , let 2A = 30
cos30 = 2cos^2 15 - 1
solving this for cos 15 I got √(√3 + 2)/2
now use the other expansion for cos 2A
cos 2A = 1 - 2sin^2 A
cos 15 = 1 - 2sin^2 7.5
this gave me
2sin^2 7.5 = 1 - √(√3 + 2)/2
sin 7.5 = √[2 - √(√3 + 2) ]/2
you can check it with sin 7.5 on your calculator, it is correct.
Trig - How do i find the exact value of sin 15 using the half angle formula
trig - find the exact value given that cosA=(1/3) in quad I, sin B=(-1/2) in ...
trig - Solving Trig Functions: How Do You Solve For Sin 7.5 Using Half-Angle and...
Trig - Use the half angle formula to find the exact value of tan 7 pie/8
trig - find the exact value by using the appropriate half-angle identity: sin(...
trig - use a half angle formula to find the exact value of cos 75 degree
trig - Use a half-angle formula to find the exact value of cos 5ð/12
Math - Use a half angle formula to determine the exact value of sin 7(pi)/12.
Trigonometry - use the appropriate trig identity (sum and difference, half angle...
trig - I asked below but I guess it was not understood what I was asking. I'...
For Further Reading