Writing quadratic equations from 3 points

Denis

Math Team
Oct 2011
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1,026
Ottawa Ontario, Canada
Joe, are you a student attending math classes?
 

skeeter

Math Team
Jul 2011
3,363
1,854
Texas
x-intercepts are (2,0) and (-2,0) ...

$y=k(x-2)(x+2)$

y-intercept is (0,12) ...

$12=k(0-2)(0+2) \implies k = -3$

$y=-3(x-2)(x+2)$

expand to get the quadratic in standard form ...
 
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Feb 2016
377
10
seattle
Joe, are you a student attending math classes?
I am but my learning style is getting in the way and it is a challenge. How we are being taught is much different than our previous teachers. I don't think we are being shown how to solve the problems like the ones shown here. We get a lecture but no hands on experience until we get the homework.
 
Feb 2016
377
10
seattle
x-intercepts are (2,0) and (-2,0) ...

$y=k(x-2)(x+2)$

y-intercept is (0,12) ...

$12=k(0-2)(0+2) \implies k = -3$

$y=-3(x-2)(x+2)$

expand to get the quadratic in standard form ...
Thanks as always skeeter!!! So guessing the -3 came from adding the -2 and the 2 together and then dividing the 12 by it?
 
Last edited:

skeeter

Math Team
Jul 2011
3,363
1,854
Texas
Thanks as always skeeter!!! So guessing the -3 came from adding the -2 and the 2 together and then dividing the 12 by it?
no, by multiplying (-2)(2) = -4 , then dividing 12 by -4

... adding (-2) and (2) results in zero.