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# Hello , how come this works? (trig question) Watch

1. Hello , how come sin(-pi*b) can be written as -sin(pi*b). I thought we couldn't move around things inside the brackets of trig functions? pls help ? thanks for any help in advance!
2. Sketch the graph of y = sin x and consider the symmetry?
3. (Original post by laurawoods)
Hello , how come sin(-pi*b) can be written as -sin(pi*b). I thought we couldn't move around things inside the brackets of trig functions? pls help ? thanks for any help in advance!
Normally you can't, you're right.
A general point:

Also
4. (Original post by Mr M)
Sketch the graph of y = sin x and consider the symmetry?
It would be reflected in the line y axis right?
5. (Original post by laurawoods)
It would be reflected in the line y axis right?
That is the graph of so no. Could you draw it from -360 degrees to 360 degrees and it will answer your question?
6. (Original post by Mr M)
That is the graph of so no. Could you draw it from -360 degrees to 360 degrees and it will answer your question?
Hello, yes what I did is I drew, the graph of sinx , then drew the other two sin(-x) and -sin(x). The latter two are the same , isn't it ? But what I was wondering is: are we meant to know this or not? It seems obvious that they are the same when the graph is constructed, but otherwise how are we meant to know this simply by looking at it? Because one of the question I saw in a paper required the use of this knowldeg/
7. (Original post by laurawoods)
Hello, yes what I did is I drew, the graph of sinx , then drew the other two sin(-x) and -sin(x). The latter two are the same , isn't it ? But what I was wondering is: are we meant to know this or not? It seems obvious that they are the same when the graph is constructed, but otherwise how are we meant to know this simply by looking at it? Because one of the question I saw in a paper required the use of this knowldeg/
There are two rules you ought to learn.

because cos is an even function

because sin is an odd function

http://www.mathsisfun.com/algebra/fu...-odd-even.html
8. (Original post by Mr M)
There are two rules you ought to learn.

because cos is an even function

because sin is an odd function

http://www.mathsisfun.com/algebra/fu...-odd-even.html
hello ! does odd and even functions come under edexcel too? because i don't remember learning them at all?
9. (Original post by laurawoods)
hello ! does odd and even functions come under edexcel too? because i don't remember learning them at all?
Whilst the terms odd and even aren't explicitly used I think those two examples are required for edexcel.
10. (Original post by laurawoods)
hello ! does odd and even functions come under edexcel too? because i don't remember learning them at all?
It is just general mathematical knowledge. I have no idea whether Edexcel would expect you to be aware of them but it isn't hard and you have seen them now.
11. (Original post by laurawoods)
hello ! does odd and even functions come under edexcel too? because i don't remember learning them at all?
It comes up in C2 edexcel so I suspect its a prerequisite from AS level knowledge
12. (Original post by Mr M)
It is just general mathematical knowledge. I have no idea whether Edexcel would expect you to be aware of them but it isn't hard and you have seen them now.
cool thanks!
13. another way to look at this also is, it might also help to see this if you use the formula for to expand:

= =

=

=

14. (Original post by Mr M)
It is just general mathematical knowledge. I have no idea whether Edexcel would expect you to be aware of them but it isn't hard and you have seen them now.
PLease, can u explain this to me:
http://www.thestudentroom.co.uk/show...4#post42228154

Ten of them tried to help me /..but i am not understanding!

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