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Author Topic: I broke maths.  (Read 15473 times)  Share 

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Hutchoo

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I broke maths.
« on: March 26, 2011, 05:17:10 pm »
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This question is probably simple; but I don't get it and my textbook (Heinemann, Methods 1/2) doesn't explain it very well.


[IMG]http://img101.imageshack.us/img101/3900/nubquestion.png[/img]



Thanks guys.
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Russ

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Re: I broke maths.
« Reply #1 on: March 26, 2011, 05:23:48 pm »
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Take the common factor of 2 out


Choose numbers that multiply to -4 and add to +3 (+4/-1)


Graph, noting the dilation (that's why the domain is limited at -2, not -1)
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Hutchoo

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Re: I broke maths.
« Reply #2 on: March 26, 2011, 05:36:08 pm »
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Thanks for that, Russ. I found the x and y intercepts, but how would you find the turning point?
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Russ

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Re: I broke maths.
« Reply #3 on: March 26, 2011, 05:40:46 pm »
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Halfway between the two x-intercepts is the x coordinate of the turning point, substitute that into the equation for the y coordinate. Or more fancily:


Alternatively, you can derive and get:


Set it equal to 0 and solve







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|ll|lll|

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Re: I broke maths.
« Reply #4 on: March 26, 2011, 05:51:55 pm »
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Just complete the square to get into turning point form.
y = 2(x^2 + 3x -4)
y = 2[(x+3/2)^2 -9/4 -4]
y = 2[(x+ 3/2)^2 -25/4]
y = 2(x + 3/2)^2 - 25/2

Turning point would be at (-3/2, -25/2)
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Hutchoo

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Re: I broke maths.
« Reply #5 on: March 26, 2011, 06:51:24 pm »
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Thanks, I got that answer pretty easily after that..
How about this one? As you can see, it's the same question, just a different equation to solve.

[IMG]http://img829.imageshack.us/img829/5050/aaavb.png[/img]

I know how to find the turning point but that's it.. (besides starting from 5 on the y axis)
« Last Edit: March 26, 2011, 07:01:28 pm by Hutchoo »
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aznxD

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Re: I broke maths.
« Reply #6 on: March 26, 2011, 06:59:42 pm »
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Quadratic formula or complete the square.
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onur369

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Re: I broke maths.
« Reply #7 on: March 26, 2011, 07:05:55 pm »
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You can find the derviative and then sub in the value to find the y value of the tp.
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nacho

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Re: I broke maths.
« Reply #8 on: March 26, 2011, 07:06:44 pm »
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Quote from: onur369 on March 26, 2011, 07:05:55 pm
You can find the derviative and then sub in the value to find the y value of the tp.
he's in year 11, i do not think they would have covered that in yet
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onur369

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Re: I broke maths.
« Reply #9 on: March 26, 2011, 07:07:06 pm »
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Quote from: nacho on March 26, 2011, 07:06:44 pm
Quote from: onur369 on March 26, 2011, 07:05:55 pm
You can find the derviative and then sub in the value to find the y value of the tp.
he's in year 11, i do not think they would have covered that in yet

I just realized :)
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Hutchoo

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Re: I broke maths.
« Reply #10 on: March 26, 2011, 07:11:50 pm »
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Quote from: nacho on March 26, 2011, 07:06:44 pm
Quote from: onur369 on March 26, 2011, 07:05:55 pm
You can find the derviative and then sub in the value to find the y value of the tp.
he's in year 11, i do not think they would have covered that in yet
Yeah, don't really know derivatives etc. yet.
Can someone show me how to find the x-intercepts with quad formula etc? I'm a bit lost.
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iNerd

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Re: I broke maths.
« Reply #11 on: March 26, 2011, 07:19:37 pm »
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Quote from: Hutchoo on March 26, 2011, 07:11:50 pm
Quote from: nacho on March 26, 2011, 07:06:44 pm
Quote from: onur369 on March 26, 2011, 07:05:55 pm
You can find the derviative and then sub in the value to find the y value of the tp.
he's in year 11, i do not think they would have covered that in yet
Yeah, don't really know derivatives etc. yet.
Can someone show me how to find the x-intercepts with quad formula etc? I'm a bit lost.
What don't you get exactly? Sub the values a, b and c into the formula? Do you know the formula?
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Hutchoo

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Re: I broke maths.
« Reply #12 on: March 26, 2011, 07:25:09 pm »
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I thought I knew the quad formula off by heart, but I didn't .. That's why I kept getting it wrong.
Well, assuming I've done everything right so far; I've gotten:

What do I do after that :/?
« Last Edit: March 26, 2011, 07:28:25 pm by Hutchoo »
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iNerd

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Re: I broke maths.
« Reply #13 on: March 26, 2011, 07:28:32 pm »
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Quote from: Hutchoo on March 26, 2011, 07:25:09 pm
I thought I knew the quad formula off by heart, but I didn't .. That's why I kept getting it wrong.
Well, assuming I've done everything right so far; I've gotten:

What do I do after that :/?
simplify root24.
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Hutchoo

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Re: I broke maths.
« Reply #14 on: March 26, 2011, 07:34:18 pm »
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, yes?

I don't know if I'm doing this right :/
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