# A level maths trig question help!

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Hi I am finding these questions difficult any help would be appreciated.

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#3

Try using the sin^2x cos^2x = 1 rule to eliminate factors for the equation. You might be able to, say, hey rid of a cos^2x somewhere,or something.

Last edited by JustACoincidence; 1 year ago

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(Original post by

Try using the sin^2x cos^2x = 1 rule to eliminate factors for the equation. You might be able to, say, hey rid of a cos^2x somewhere,or something.

**JustACoincidence**)Try using the sin^2x cos^2x = 1 rule to eliminate factors for the equation. You might be able to, say, hey rid of a cos^2x somewhere,or something.

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#5

Bottom question should be quite simple.

For any/most "show that" questions, generally start with the expression on the LHS, then do the obvious algebra until you get the expression given to you on the RHS.

In this case, the 'obvious' thing is to square the bracket.

Top questions require a couple of steps at least.

First of all, you should be able to solve a trig eqn of the form

4sin(3x-20) = 0.7 , for example.

or

4cos(3x-20) = 0.7 ,

or

4tan(3x-20) = 0.7.

or

3sin^2(3x-20) - 4sin(3x-20) + 1 = 0

ie equations with just

When there's more than one trig function involved, you'll nearly always need to use a trig ident.

For any/most "show that" questions, generally start with the expression on the LHS, then do the obvious algebra until you get the expression given to you on the RHS.

In this case, the 'obvious' thing is to square the bracket.

Top questions require a couple of steps at least.

First of all, you should be able to solve a trig eqn of the form

4sin(3x-20) = 0.7 , for example.

or

4cos(3x-20) = 0.7 ,

or

4tan(3x-20) = 0.7.

or

3sin^2(3x-20) - 4sin(3x-20) + 1 = 0

ie equations with just

**one**trig function involved. Can you handle**those**?When there's more than one trig function involved, you'll nearly always need to use a trig ident.

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#6

**JustACoincidence**)

Try using the sin^2x cos^2x = 1 rule to eliminate factors for the equation. You might be able to, say, hey rid of a cos^2x somewhere,or something.

sin

^{2}x + cos

^{2}x ≡ 1

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#7

(Original post by

Hi I am finding these questions difficult any help would be appreciated.

Attachment 789944

**Realdon66**)Hi I am finding these questions difficult any help would be appreciated.

Attachment 789944

Last edited by MathsLove; 1 year ago

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#8

(Original post by

If you have invested a little effort on it, this is pretty straightforward question. Have you covered double angle formulae? Do you know how to write tan(x) in terms of sine and cosine ?

**MathsLove**)If you have invested a little effort on it, this is pretty straightforward question. Have you covered double angle formulae? Do you know how to write tan(x) in terms of sine and cosine ?

6 is straightfoward when using the right trig identity which above posters have recognised correctly.

7 may be 'harder' to spot, but it's simply double angle formula.

What are your workings so far?

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#9

7 doesn’t have to be double angle... you can spot it in first two lines!!

For 7- Try expanding the LHS see what you get, and use the identity sinx cosx=1

For 6 - use the identity sinx cosx=1 to re arrange some of the terms so that you have them just in terms of cos or sin, then compare with a quadratic and see what to do from there

Although I feel like I’m missjng something but why the above posters are talking about double angle formula, you can literally solve all these questions with the sin^2x cos^2x = 1 identity just rearranging it

For 7- Try expanding the LHS see what you get, and use the identity sinx cosx=1

For 6 - use the identity sinx cosx=1 to re arrange some of the terms so that you have them just in terms of cos or sin, then compare with a quadratic and see what to do from there

Although I feel like I’m missjng something but why the above posters are talking about double angle formula, you can literally solve all these questions with the sin^2x cos^2x = 1 identity just rearranging it

Last edited by timif2; 1 year ago

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#10

(Original post by

Although I feel like I’m missjng something but why the above posters are talking about double angle formula, you can literally solve all these questions with the sin^2x cos^2x = 1 identity just rearranging it

**timif2**)Although I feel like I’m missjng something but why the above posters are talking about double angle formula, you can literally solve all these questions with the sin^2x cos^2x = 1 identity just rearranging it

These 3 qns are first year A-Level. None of that requires combination angles, or dble angle formulas.

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(Original post by

Bottom question should be quite simple.

For any/most "show that" questions, generally start with the expression on the LHS, then do the obvious algebra until you get the expression given to you on the RHS.

In this case, the 'obvious' thing is to square the bracket.

Top questions require a couple of steps at least.

First of all, you should be able to solve a trig eqn of the form

4sin(3x-20) = 0.7 , for example.

or

4cos(3x-20) = 0.7 ,

or

4tan(3x-20) = 0.7.

or

3sin^2(3x-20) - 4sin(3x-20) + 1 = 0

ie equations with just

When there's more than one trig function involved, you'll nearly always need to use a trig ident.

**begbie68**)Bottom question should be quite simple.

For any/most "show that" questions, generally start with the expression on the LHS, then do the obvious algebra until you get the expression given to you on the RHS.

In this case, the 'obvious' thing is to square the bracket.

Top questions require a couple of steps at least.

First of all, you should be able to solve a trig eqn of the form

4sin(3x-20) = 0.7 , for example.

or

4cos(3x-20) = 0.7 ,

or

4tan(3x-20) = 0.7.

or

3sin^2(3x-20) - 4sin(3x-20) + 1 = 0

ie equations with just

**one**trig function involved. Can you handle**those**?When there's more than one trig function involved, you'll nearly always need to use a trig ident.

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#12

(Original post by

When dealing with proof questions, ... hence you get 1+2sinxcosx as required

**Azim Patel**)When dealing with proof questions, ... hence you get 1+2sinxcosx as required

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#13

(Original post by

Would you mind telling me the steps to get to the answer. In class, we’ve done trig identities but haven’t applied it to these types of questions (yet) Much appreciated!

**Realdon66**)Would you mind telling me the steps to get to the answer. In class, we’ve done trig identities but haven’t applied it to these types of questions (yet) Much appreciated!

So it's not like you have a lot of choices what to do - you just have to apply the identity..

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#14

**Realdon66**)

Would you mind telling me the steps to get to the answer. In class, we’ve done trig identities but haven’t applied it to these types of questions (yet) Much appreciated!

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#15

**Realdon66**)

Would you mind telling me the steps to get to the answer. In class, we’ve done trig identities but haven’t applied it to these types of questions (yet) Much appreciated!

I'll add more to what's already been given by me and others after you've shown/explained what you've attempted so far.

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