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# C3 identities help. watch

1. Solve for 0 >(or equal) x < 2pi

Sin 2x = cos 2x

The mark scheme says tan 2x = 1, now i understand if you divide them both you'd get tan 2x but where does the 1 come from?

2. If you divide sin2x by cos2x you get tan2x
but you also have to divide cos2x by cos2x which equals 1.
( what you do to one side you must do to the other etc)
3. If you divide through by on both sides of the equation then you end up with on the LHS and 1 on the RHS... since (except when ).
4. I'm doing the same question now!

I'd like to ask, once having done tan2∅=1

and ∅ = 22.5, 202.5

Where do the other two solutions come from?

I will convert back to radians in the end...

Thank you
5. (Original post by gottastudy)
I'm doing the same question now!

I'd like to ask, once having done tan2∅=1

and ∅ = 22.5, 202.5

Where do the other two solutions come from?

I will convert back to radians in the end...

Thank you
loool

It's 2x therefore you'll have to divide the final answer by 2 at the end.
So instead of finding the values for 0 to 360 find them to 720, then when you divide them by 2 so you get x not 2x, you'll get the real values.

Only state the final values within the original range 0 to 360 though.
Do you understand what i mean?
6. You get 1 by dividing 2 of the same terms. cos2x/cos2x=1 or in any case x/x=1

^ Because it's 2theta it's 2 x 360=720 degrees, so you go around again, then divide by 2 to get theta
7. (Original post by gottastudy)
I'm doing the same question now!

I'd like to ask, once having done tan2∅=1

and ∅ = 22.5, 202.5

Where do the other two solutions come from?

I will convert back to radians in the end...

Thank you
Firstly it's in radians so you should get 1/4pi and 5/4pi then the other 2 would be 2pi + 1/4pi and 3pi + 1/4pi

which will give 2x = 1/4pi, 5/4pi, 9/4pi, 13/4pi
x = 1/8pi, 5/8pi, 9/8pi and 13/8pi
8. (Original post by Spongebob*No*Pants)
loool

It's 2x therefore you'll have to divide the final answer by 2 at the end.
So instead of finding the values for 0 to 360 find them to 720, then when you divide them by 2 so you get x not 2x, you'll get the real values.

Only state the final values within the original range 0 to 360 though.
Do you understand what i mean?
Thank you rep when it resets

hold on....i think I have it now...

Is it:

2∅ = 720

45 + 360 (whole cycle) = 405 = 2∅
225 + 360 = 585 = 2∅

Then divide by 2, to get ∅?
9. (Original post by gottastudy)
Thank you rep when it resets

hold on....i think I have it now...

Is it:

2∅ = 720

45 + 360 (whole cycle) = 405 = 2∅
225 + 360 = 585 = 2∅

Then divide by 2, to get ∅?

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