Use a double-angle identity to find the exact value of each expression.cos4π/3; this is what I got then I was stuck. cos2(2π/3)=1-2sin^2theta but I don't know what sin^2(2π/3) is.

Question

anonymous · Answer

@ajprincess  please help me :)

ajprincess · Answer

sin(2pi/3)=sqr3/2
so sin^2(2pi/3)=(sqrt3/2)^2=3/4

anonymous · Answer

ahh thank you!

ajprincess · Answer

sin(2pi/3)=sin120

ajprincess · Answer

yw.

anonymous · Answer

so cos(4pi/3) = cos2(2pi/3)= 1-2sin^2(2pi/3)=1-2(3/4)=-1/2?

ajprincess · Answer

yes.

anonymous · Answer

i have another one  if you dnt mind?

ajprincess · Answer

sure post t

anonymous · Answer

^^ thx; use the half angle identity to find sin(5pi/6); this is how far i got. sin(5pi/6)=sin[(10pi/12)/2] then i was lost. :s

anonymous · Answer

write an equation in slope intercept form of the line that satisfies the followin condition. x-intercept 12 and y-intercept 14

ajprincess · Answer

This may be of some use to u.

ajprincess · Answer

sin(5pi/6)=sin2(5pi/12)
see if u can do nw.

anonymous · Answer

okay, lemme try :)

anonymous · Answer

@ajprincess  how did you get sin(5pi/6)=sin2(5pi/12)? because if I look at the half-angle identity for sin it says sin(x/2)=$$\pm \sqrt({1+cosx})/2$$ (5pi/6) x2 = 10pi/6=5pi/3

ajprincess · Answer

am so sorry. i thought it as double angle identity

anonymous · Answer

its okay, I found the answer: my sin(5pi/6) x 2 was wrong in the first one :/ silly mistake

ajprincess · Answer

fine then.