Question

express sin 60 - sin 20 as a product
Any ideas of how to start it? lol

Answer 1

there are some identities for sums and differences of sines and cosines as products
they;ll be up on the web.

i think sin A - sin B = 2 sin(A+B) cos(A- B)
---- -----
2 2

but i'm not sure

Answer 2

I am using a different identity but how would you do it with that identity? @welshfella I am not finding a formula like that either lol

Answer 3

http://www.clarku.edu/~djoyce/trig/identities.html

Answer 4

@welshfella we havent learned those identities in class however

Answer 5

mine was wrong its 2 cos (A+B) sin (a-B)
-- --
2 2

Answer 6

@welshfella anything else that would work with it?

Answer 7

well i suppose you can do this

sin 40 = sin ( 2*20) = 2 sin 20 cos 20

sin 40 - sin 20
= 2 sin 20 cos 20 - sin 20
= sin 20 (2 cos 20 - 1)

Answer 8

ohh - im going crazy - its sin 60 !!

Answer 9

This question I swear XD This is the formula I think is right to use

Answer 10

The second one

Answer 11

yes - thats the one i mentioned last

Answer 12

So the way you just did it is how its done?

Answer 13

Is this right how I did it?

Answer 14

yes put A = 60 and B = 20 and simplify

2 cos (60 + 20) sin (60 - 20)
------ -------
2 2

Answer 15

yes you got it

Answer 16

2 cos 40 sin 20