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# P3 graphs..... watch

1. how do u know if an equation is odd or even??
i totally forgot bout curves so i'm frantically trying 2 revise them now....its my weakest point
2. (Original post by wonkey)
how do u know if an equation is odd or even??
i totally forgot bout curves so i'm frantically trying 2 revise them now....its my weakest point
do they come in the exams coz i never saw any
3. (Original post by tammypotato)
do they come in the exams coz i never saw any
well no i haven't seen any as such.....but its in the flipping text book.....so ur guesses r as gd as mine!............
4. (Original post by wonkey)
how do u know if an equation is odd or even??
i totally forgot bout curves so i'm frantically trying 2 revise them now....its my weakest point
even function: f(-x) = f(x) , i.e. y = cosx
odd function: f(-x) = -f(x) , i.e. y = sinx ???? please could someone confirm
5. (Original post by wonkey)
well no i haven't seen any as such.....but its in the flipping text book.....so ur guesses r as gd as mine!............
i wont revise it ... that means knowing my luck its gona come up!
6. An even function satisfies f(x)=f(-x) so the graph has a line of symmetry in the y-axis. An odd function satisfies f(x)=-f(-x) so the graph has rotational symmetry around the origin. f(x)=cosx is even while f(x)=sinx is odd. (These are just examples of odd and even functions, as there are many more. For example, f(x)=x² is even as there is a line of symmetry in the y-axis while f(x)=x³ is odd as there is rotational symmetry about the origin).
7. (Original post by mockel)
even function: f(-x) = f(x) , i.e. y = cosx
odd function: f(-x) = -f(x) , i.e. y = sinx ???? please could someone confirm
i don't understand ......... explain y = cosx pls.......thx
8. (Original post by wonkey)
i don't understand ......... explain y = cosx pls.......thx
see meepmeep's post
9. (Original post by meepmeep)
An even function satisfies f(x)=f(-x) so the graph has a line of symmetry in the y-axis. An odd function satisfies f(x)=-f(-x) so the graph has rotational symmetry around the origin. f(x)=cosx is even while f(x)=sinx is odd.
why is f(x) = cos x even?? wot would f(-x) be for that?? i don't get how u work it out.....sorry, i've never actually understood f(x) becoming f(-x) from P2, lol
10. (Original post by wonkey)
why is f(x) = cos x even?? wot would f(-x) be for that?? i don't get how u work it out.....sorry, i've never actually understood f(x) becoming f(-x) from P2, lol
ohhhhh i get it......so put in the same number but in its negative form, and answer will still be the same?! thank uuuuuuu
11. (Original post by wonkey)
why is f(x) = cos x even?? wot would f(-x) be for that?? i don't get how u work it out.....sorry, i've never actually understood f(x) becoming f(-x) from P2, lol
basically, if you put in a value of x, you'll get the same result as putting in -x
e.g. y=cosx, if x=60, y=0.5
if x=-60, y=0.5, still
12. (Original post by wonkey)
why is f(x) = cos x even?? wot would f(-x) be for that?? i don't get how u work it out.....sorry, i've never actually understood f(x) becoming f(-x) from P2, lol
If f(x) = cosx, f(-x) = cos(-x) = cos(0-x) = cos0cosx - sin0sinx = cosx so f(x) = f(-x) so f(x) is an even function
13. (Original post by wonkey)
ohhhhh i get it......so put in the same number but in its negative form, and answer will still be the same?! thank uuuuuuu
Yep, you've got it. Whereas if it's odd, then when you put the neagtive number in, the answer you get is the same but negative (eg sin pi/2=1 and sin -pi/2=-1).

From this, you get cos(x)=cos(-x) and -sin(x)=sin(-x)
14. okay, well i'm off to school now....p1 at 1.00, followed by p3 at around 2.30....should be interesting
good luck to everyone, and i'll be talking to you all at around 5.00 (when i come home)
15. (Original post by wonkey)
ohhhhh i get it......so put in the same number but in its negative form, and answer will still be the same?! thank uuuuuuu
You have to be a bit careful if you do it this way as sin(pi) = sin(-pi) but sine is an odd function. With trig functions it's probably easiest to consider the graphs and decide if they're symmetrical in y axis or have rotational symmetry 180 degrees about the origin.
16. (Original post by Bezza)
You have to be a bit careful if you do it this way as sin(pi) = sin(-pi) but sine is an odd function. With trig functions it's probably easiest to consider the graphs and decide if they're symmetrical in y axis or have rotational symmetry 180 degrees about the origin.
Yeah, to be totally correct I should have wrote that:

For an even function f(x)=f(-x) (the three lines means "is identically equal" so it holds for all values of x) so has a line of symmetry through the y-axis and for an odd function -f(x)=f(-x) so has rotational symmetry around the origin.
17. (Original post by mockel)
okay, well i'm off to school now....p1 at 1.00, followed by p3 at around 2.30....should be interesting
good luck to everyone, and i'll be talking to you all at around 5.00 (when i come home)
yeah same, i'm resitting P1....best of luck
18. (Original post by Bezza)
You have to be a bit careful if you do it this way as sin(pi) = sin(-pi) but sine is an odd function. With trig functions it's probably easiest to consider the graphs and decide if they're symmetrical in y axis or have rotational symmetry 180 degrees about the origin.
thx for advice bezza and meep meep! much appreciated
19. (Original post by wonkey)
thx for advice bezza and meep meep! much appreciated
No trouble. Good luck with it this afternoon.

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