C3 Trig question

9

Given that

2cos(y+30) = (root3)sin(y-30)

find the value of tan y in the form k(root3) where k is a rational constant.

I don't have a clue how to do do this, especially becaue the brackets are different so you can't just divide sin by cos :smile:

Any help would be nice :smile:

Thanks

PS: Does anyone know how you get square root signs on here? :biggrin:

Reply 1

fusionskd

10

What exam board are you with?

Reply 2

Hearing Voices

OP

9

Ocr

Reply 3

fusionskd

10

I dont get what you mean by in the form k(root3)...root3 of what?

Reply 4

generalebriety

16

fusionskd

I dont get what you mean by in the form k(root3)...root3 of what?

Sigh... root 3. You know,

\sqrt{3}

.

Try expanding out the sin/cos. You know the sin(A-B) and cos(A+B) formulas, right? You also should know sin 30 and cos 30...

Reply 5

fusionskd

10

LOL I thought he meant cube root....My mistake :s-smilie:

Reply 6

fusionskd

10

2(cosycos30 - sinysin30) = (root3)(sinycos30 - cosysin30)

2(cosy([root3]/2) - [siny]/2) = (root3)(siny([root3]/2) - [cosy]/2)

Thats how you start off...then you simplify etc to get tan y = the result. If its hard to understand write it out.

Reply 7

generalebriety

16

fusionskd

2(cosycos30 - sinysin30) = (root3)(sinycos30 - cosysin30)

2(cosy([root3]/2) - [siny]/2) = (root3)(siny([root3]/2) - [cosy]/2)

Thats how you start off...then you simplify etc to get tan y = the result. If its hard to understand write it out.

Don't mean to be rude, but could you stop giving away the answer? We're meant to be helping people, not spoonfeeding them; see the posting guidelines. :smile:

Reply 8

fusionskd

10

generalebriety

Don't mean to be rude, but could you stop giving away the answer? We're meant to be helping people, not spoonfeeding them; see the posting guidelines. :smile:

I just started it off. In c3 you dont learn the sin(a+b) or cos(a+b) formulae, you do so in c4 which is why I tryed to show how it was applied. But in future i'll try not to give away the answer then... :s-smilie:

Reply 9

Hearing Voices

OP

9

I have done those formulae... so it must be different for different boards.

Thanks for the help everyone :smile:

Reply 10

generalebriety

16

fusionskd

In c3 you dont learn the sin(a+b) or cos(a+b) formulae, you do so in c4 which is why I tryed to show how it was applied.

You do learn those formulas in C3, at least for my exam board you did; otherwise they wouldn't have set the question. :wink:

Reply 11

fusionskd

10

Lol fair enough...but that didnt stop the stupid assignments we had for c3. Once in a while [not always] it would involve something to do with c4 which we didnt have a clue on at the time. They used exam pro to compile the assignments and some questions are pretty old..

C3 Trig question

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