Maths Hw

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junglemonkey
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Maths Hw

Post by junglemonkey »

Ok, just started my higher course. I'm confuddled already. This is a really confusing post, good luck to anyone who can decipher this. Even if you can't, please reply saying something so I know it's been read lol :)



This is about compositions of functions



I know how to substitute into a function and basically everything up to standard grade. For example:



f(x) = 2x + 1

f(2) = 5



lol i bet I got that wrong.

But now we've moved on to compositions of functions. If you had this would you just substitute in the same way?



f(x) = 2/(x+1) g(x) = (2/x) -1 (I've put in the brackets because in f(x) the denominator is x + 1 but in g(x) the denominator is x)



So to find f(g(x)) and find g(f(x)) would you subsitute in like this? ( a fraction in brackets just indicates the part that is actually in the fraction, it's hard to do this over the internet'



f(g(x)) = f((2/x)-1) (ie. Substitute in the g(x) equation)

f = 2/(2/x)-1 + 1

f = 2/(2/x)

f=x





Please say I am doing this right and you just substitute the other function for x, as if it were any other number or whatever? Damn that was confusing.



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Re: Maths Hw

Post by faith »

wow i left this post feeling 10 times stupider......
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Re: Maths Hw

Post by junglemonkey »

Lol don't, I understand it just as little as you :)



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Re: Maths Hw

Post by noxor »

yeah, you're doing it right, both answers are x
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Re: Maths Hw

Post by junglemonkey »

Is the last bit definitely right?



2/2x - is it x?



How is that?



I was torn between x and 1/x ... And I don't fully understand how I got that. is it because the 2 divides into the 2 on the numerator, but, it was 2 TIMES 2, so i becomes 1x?
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Re: Maths Hw

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yes
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Re: Maths Hw

Post by diane2ns »

I got x, and I know IO'm doing it right, I better be, I go to a math academy.
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Re: Maths Hw

Post by noxor »

Originally posted by junglemonkey@Jun 15 2003, 01:51 PM

Is the last bit definitely right?

but, it was 2 TIMES 2, so i becomes 1x?


it was 2 * 2?



2/(2/x) means 2 * x / 2 (division is reciprical multiplication)



in other words,



2 * (1/2) * x and not 2 * 2 / x or 2 * (1/2) / x
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Re: Maths Hw

Post by junglemonkey »

Crap. Typo. I meant 2 TIMES X lol.
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Re: Maths Hw

Post by DreamPixie »

f(x) = 2/(x+1) g(x) = (2/x) -1

f(g(x)) = 2/(((2/x)-1)+1)

= 2/(2/x)

= 1/(1/x) = x

ok, my bad, i got 1/x the first time, but you're right :) <3
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Re: Maths Hw

Post by Jaegermeister »

That's the idea of the equations, you've done them rihgt.



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Re: Maths Hw

Post by Becoming Human »

Nice. It looks like everything is right to me.



When you get something like F(G(x)) just think:



What is the answer to G(x) plugged into the F function.



But it looks like you've got that concept already, so good job.
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Re: Maths Hw

Post by junglemonkey »

I under stand now why it is X



If you write this:

f = 2/(2/x) ... And you write it in linear form it becomes clearer because to divide by a fraction you turn it upside down and multiply, therefore the x is not 1/x ...



2/(2/x)

= 2 x (x/2)

= 2x/2 (the twos now cancel)

= x



I've totally got it now :P



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Re: Maths Hw

Post by DownInFlames »

OMG! I hate algebra with all my heart! When school starts again, I'll have to post one of these with all my problems so you guys can do them for me. I am NOT looking forward to Algebra 2!
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Re: Maths Hw

Post by junglemonkey »

Originally posted by MyOwnPerson@Jul 11 2003, 06:35 PM

OMG! I hate algebra with all my heart! When school starts again, I'll have to post one of these with all my problems so you guys can do them for me. I am NOT looking forward to Algebra 2!


Lol since I'm not american i have no idea what Algebra 2 is!



I think once you have a good basic understanding of these type of problems, and you can work through them, and check the answers and they're right (sometimes lol) it's extremely satisfying. I went through a long while doing really bad in maths and I mean REALLY bad... And now I'm quite good at it even though we're going on to very hard stuff after summer.



So, MyOwnPerson, hold out and try hard :)
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