Question

Prove , cos20cos40cos80=1/8 . Angles are in degrees .

Answer 1

blue?

Answer 2

Blue what?

Answer 3

?

Answer 4

blue is the answer

Answer 5

ok

Answer 6

What the??

Answer 7

Let cos20*cos40*cos80 = U.

Therefore 8*U*sin20
= 4*(2*sin20*cos20)*cos40*cos80
= 4*sin(2*20)*cos40*cos80 [since sin2A = 2*sinA*cosA]
= 2*(2*sin40*cos40)*cos80
= 2*sin(2*40)*cos80
= 2*sin80*cos80
= sin(2*80)
= sin160
= sin(180-20)
= sin20 [since sin(180-x) = sin(x)]

So U = (sin20)/(8*sin20) = 1/8

Answer 8

calm down Erkot:)

Answer 9

Grammatical mistake . My bad . Thank you !

Answer 10

:)

Answer 11

guess where i am blue?

Answer 12

lab?