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# Rcos(0-a) Help | acosx+bsinx | watch

1. Where have i gone wrong?
Show that L.H.S can be written as R.H.S ..........x is meant to be theta

(cosx-sinx)(17cosx-7sinx) = 5cos2x-12sin2x+c

- think this is wrong

2. (Original post by joyoustele)
Where have i gone wrong?
Show that L.H.S can be written as R.H.S ..........x is meant to be theta

(cosx-sinx)(17cosx-7sinx) = 5cos2x-12sin2x+c

- think this is wrong

Check that the 4th line of working expands to give the 3rd line - you've made a small mistake.

Then use , which is one of the forms of the identity that you'll need to know. I'm not sure why you've expanded again in your final line.
3. (Original post by Notnek)
Check that the 4th line of working expands to give the 3rd line - you've made a small mistake.

Then use , which is one of the forms of the identity that you'll need to know. I'm not sure why you've expanded again in your final line.

Then?..........
4. (Original post by joyoustele)

Then?..........
Well you could just rearrange this identity

to make the subject and then just sub that in. That's one way of doing it.
5. (Original post by Notnek)
Well you could just rearrange this identity

to make the subject and then just sub that in. That's one way of doing it.
Wow, never thought of that

(Original post by joyoustele)
Where have i gone wrong?
Show that L.H.S can be written as R.H.S ..........x is meant to be theta

(cosx-sinx)(17cosx-7sinx) = 5cos2x-12sin2x+c

- think this is wrong

Attached Images

7. (Original post by gurungg48)
Nice, what tool did you use when answering the question?
8. (Original post by joyoustele)
Nice, what tool did you use when answering the question?
I Use Idroo. Its really good. I use this to teach online too.

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