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# C4 Trigonometry help watch

1. If you are given a equation like 4cosx+2sinx=3

Do you use
RSin(ϴ+α) or
RSin(ϴ -α) or
RCos(ϴ+α) or
RCos(ϴ-α)

Can someone explain when to use each one thanks!
2. (Original post by aceplayyt)
If you are given a equation like 4cosx+2sinx=3

Do you use
RSin(A+B) or
RSin(A-B) or
RCos(A+B) or
RCos(A-B)

Can someone explain when to use each one thanks!
Any works, as long as it's done correctly.
3. (Original post by aceplayyt)
If you are given a equation like 4cosx+2sinx=3

Do you use
RSin(ϴ+α) or
RSin(ϴ -α) or
RCos(ϴ+α) or
RCos(ϴ-α)

Can someone explain when to use each one thanks!
Any can be used and they will give you the same thing in different forms.

But an exam will usually tell you which one to use.
4. (Original post by aceplayyt)
If you are given a equation like 4cosx+2sinx=3

Do you use
RSin(ϴ+α) or
RSin(ϴ -α) or
RCos(ϴ+α) or
RCos(ϴ-α)

Can someone explain when to use each one thanks!
You have to make the signs match up

E.g Don't use RCos(ϴ+α) for + sign question since Cos(ϴ+α) = cosϴcosα - sinαsinϴ
5. (Original post by G.Y)
You have to make the signs match up

E.g Don't use RCos(ϴ+α) for + sign question since Cos(ϴ+α) = cosϴcosα - sinαsinϴ
Yeah you can. You can use any as long as you make the coefficient positive or negative accordingly.
Yeah you can. You can use any as long as you make the coefficient positive or negative accordingly.
But it's simpler not to? Why overcomplicate

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