Question

Rewrite with only sin x and cos x.

sin 3x

Answer 1

@hartnn

Answer 2

@iPwnBunnies

Answer 3

medal!!

Answer 4

i just did it and got 2 sin x cos2x + cos x

Answer 5

but the cosx might be wrong

Answer 6

it might be sin^3x..?

Answer 7

Really?

\(\sin(3x) = \sin(x + 2x) = \sin(x)\cos(2x)+\cos(x)\sin(2x)\)

Now what?

Answer 8

\[\sin 3x=\sin \left( 2x+x \right)=\sin 2x \cos x+\cos 2x \sin x\]

Answer 9

i dont get it

Answer 10

i dont get what i have to do next

Answer 11

\(\sin(2x) = ???\)

\(\cos(2x) = ???\)

There is a reasona why you studied all those identities? Now is the time to prove it.

Answer 12

\[\sin 2x=\sin \left( x+x \right)=\sin x \cos x+\cos x \sin x=2\sin x \cos x\]
\[\cos 2x=\cos \left( x+x \right)=\cos x~\cos x+\sin x~\sin x=\cos ^2x-\sin ^2x\]

Answer 13

substitute and simplify

Answer 14

thank you @surjithayer

Answer 15

now i add them?

Answer 16

what do i do now?.... @surjithayer

Answer 17

?? What are you not seeing? Did you go through the steps so far provided? We have seen none of YOUR work. This would be a good time to demonstrate your algebra skills. Apply the identities. Simplify where you can. There is nothing magic about it.

Answer 18

@mathslover

Answer 19

I DO NOT SEE WHAT I HAVE TO DO NEXT. WHAT DONT YOU UNDERSTAND?

Answer 20

@tkhunny

Answer 21

@uri

Answer 22

Did you substitute the identities? If not, that is what you do next.
Did you simplify where possible? If not, that is what you do next.
Did you complete the exercise? If not, that is what you do next.
Did you move on to the next problem? If not, that is what you do next - unless you want to take a lunch break, or something.

Answer 23

i got it right, soooo bye

Answer 24

Woo-hoo!!! Too bad you showed us NONE of your work. Very, VERY hard to help you if you show us nothing. I am glad you got it.