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# trigonometry exam question watch

1. (Original post by Notnek)
E.g.

becomes

You can do a similar thing here.

i that right?
2. (Original post by Notnek)
E.g.

becomes

You can do a similar thing here.
i don't get how you replaced to x inside the identity with a y?
3. (Original post by Maths&physics)
i don't get how you replaced to x inside the identity with a y?
Can you please show me which line of working you don’t understand?
4. (Original post by Notnek)
Can you please show me which line of working you don’t understand?

where did the y come from inside the identity?
5. (Original post by Maths&physics)

where did the y come from inside the identity?
The identity is

I'm using A here because I think the x/y may be confusing. This is an identity so you can replace A with anything. Back to the working:

(*)

I'm labeling the line above with a (*) to refer to it later.

Then using the identity above, you can replace A with y to give

So then the line of working (*) becomes

Then you can move the sin to the other side:

6. (Original post by Notnek)
The identity is

I'm using A here because I think the x/y may be confusing. This is an identity so you can replace A with anything. Back to the working:

(*)

I'm labeling the line above with a (*) to refer to it later.

Then using the identity above, you can replace A with y to give

So then the line of working (*) becomes

Then you can move the sin to the other side:

thank you.

cos(y) doesn't = x in the cos graph, but yes, in this case it does, do you understand what i mean?

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