Question

sin20*sin40*sin80=?

Answer 1

This is the unit circle (radius=1). Solve for x=,20 x=40 and x=80. The sin is the y value.

Answer 2

There is another way to solve this, using identities.
I'd have to do it on paper, give me a minute.

Answer 3

WELCOME TO OPENSTUDY! :D

Answer 4

one more way

Answer 5

we know
sin2x=2sinx*cosx

Answer 6

@AkashdeepDeb
i have viewd your question , can you plz write the identity. Sin 20 Sin 40.
like the formula

Answer 7

@khaakenajaf
Just take it in the form of
sin A. sin B

There is an identity which says that:
2.sinA.sinB=cos(A−B)−cos(A+B)

So, to use that, just write, sin 20. sin 40 in that format by multiplying and dividing it by 2.
But, you will NOT be getting a definite answer here, you'd have to use the calculator to get cos 20.