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# Help with addition formula question watch

1. It's from Pearson's Advanced Maths A2 Core for Edexcel
pg65 Ex3C Q8b

Solve for values of x between 0° and 360°

cos(x + 45°) = cosx

I've tried to work it out but I get stuck and we didn't do a question similar to this in class to compare it to

This is my working so far but it doesn't leave me much to go off so I presume it's incorrect.
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2. (Original post by JimJam707)
...
You initially had a "cos x" on the LHS (correctly), but crossed it out for some reason and treated it as zero. Three lines up.
3. (Original post by ghostwalker)
You initially had a "cos x" on the LHS (correctly), but crossed it out for some reason and treated it as zero. Three lines up.

and then I am stuck again
4. (Original post by JimJam707)

and then I am stuck again
collect the cos elements on one side and the sin elements on the other side

then rearrange to get tan(x) = something
5. (Original post by JimJam707)

and then I am stuck again
So Now just divide by
6. (Original post by JimJam707)

and then I am stuck again

7. (Original post by Tutorsos)

The forum guidelines ask us to hint and guide - NOT to give full solutions
8. (Original post by JimJam707)
It's from Pearson's Advanced Maths A2 Core for Edexcel
pg65 Ex3C Q8b

Solve for values of x between 0° and 360°

cos(x + 45°) = cosx

I've tried to work it out but I get stuck and we didn't do a question similar to this in class to compare it to

This is my working so far but it doesn't leave me much to go off so I presume it's incorrect.
I think the simplest way to use that rule when

then the 2 cases are:

1:
or
2:
9. (Original post by ztibor)
I think the simplest way to use that rule when

then the 2 cases are:

1:
or
2:
or A=B?
10. (Original post by TenOfThem)
or A=B?
???

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