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Oh Boy! Helping my daughter with math!

post #1 of 20
Thread Starter 
OK, so my daughter is in this bizarre math class where they don't really put equations in the book. So I was helping her and I can't remember WHY I'm getting the right answer, so maybe I can get some guidance.

The question states to write the equation of a function that has x intercept of 2 and 4.

So I KNOW that it's (x-2)(x-4) = 0 or x^2 -6x + 8 = 0

But anyone remember WHY?
post #2 of 20
I feel like an dummy! That's basic math and I can't even remember how to do it! Sorry, I'm not any help at all! When DH gets home later I can ask if he knows!
post #3 of 20
Because an x intercept on the x,y graph is where y=0.

Let y=0
(x-2)(x-4) = 0
x-squared -2x - 4x + 8 = 0
x-squared - 6x + 8 = 0

Hope that helps.
post #4 of 20
well first off let me tell you you are right and that it is very understandable that this answer comes to you there isn't much work to show for it.

the intercept of a graph is where the graph crosses the axis. So we know that it crosses the x-axis at x = 2 and x = 4. Now we work backwards and we subtract two and 4 from x to get it into factored form. (x-2)(x-4) = 0. now we know to do that because of the zero product property that states(in a very misquoted way) when a function is in factored form and equal to 0 you can set each factor equal to zero and you will find the intercepts(roots) of that function. which would give you x-2 = o and x-4 = 0 and that would give you the final answer we were looking for.

I don't know what else the teacher would want.
post #5 of 20
Is that English?

post #6 of 20
Quote:
Originally Posted by butzie View Post
Because an x intercept on the x,y graph is where y=0.

Let y=0
(x-2)(x-4) = 0
x-squared -2x - 4x + 8 = 0
x-squared - 6x + 8 = 0

Hope that helps.

That didn't help me at all!

By the way, what is that funny dohicky ^ thingy mean?
post #7 of 20
Quote:
Originally Posted by AlleyGirl View Post
Is that English?

I'm not help.....either that or maybe it's German?

post #8 of 20
Quote:
Originally Posted by Natalie_ca View Post
That didn't help me at all!

By the way, what is that funny dohicky ^ thingy mean?
To the power of is what that means. x^2 means x to the second power or x * x.
post #9 of 20
Thread Starter 
Thank you!!! That's what I thought, but apparently my math mind and my language mind can't communicate with each other. I just popped out the equation without thinking of it (and she plugged it into her graphing calculator to verify that was correct.) But I couldn't really tell her why, and apparently the teacher hasn't either, LOL. I did tell her that I thought the y-intercept was -8 and that was correct as well, so at least she thinks I know what I'm doing!
post #10 of 20
oh mercy, I abhor math, I'm no help t'all. sorry
post #11 of 20
Quote:
Originally Posted by kluchetta View Post
OK, so my daughter is in this bizarre math class where they don't really put equations in the book. So I was helping her and I can't remember WHY I'm getting the right answer, so maybe I can get some guidance.

The question states to write the equation of a function that has x intercept of 2 and 4.

So I KNOW that it's (x-2)(x-4) = 0 or x^2 -6x + 8 = 0

But anyone remember WHY?
This may confuse the matter more but I believe you will find your answer here. http://ppl.nhmccd.edu/~bmagan/Parabo...tercept(s).htm
post #12 of 20
Quote:
Originally Posted by kluchetta View Post
OK, so my daughter is in this bizarre math class where they don't really put equations in the book. So I was helping her and I can't remember WHY I'm getting the right answer, so maybe I can get some guidance.

The question states to write the equation of a function that has x intercept of 2 and 4.

So I KNOW that it's (x-2)(x-4) = 0 or x^2 -6x + 8 = 0

But anyone remember WHY?
In addition to the other replies, another way of looking at it is that the statement (x-2)(x-4) = 0 is true if x is 2 or 4, and false otherwise.
post #13 of 20
Thread Starter 
Quote:
Originally Posted by Dave_L View Post
In addition to the other replies, another way of looking at it is that the statement (x-2)(x-4) = 0 is true if x is 2 or 4, and false otherwise.
Extra Credit!!!

Post the equation for the same parabola but is "upside down" to the one I found the equation to!

post #14 of 20
I am SO an English major!
post #15 of 20
Quote:
Originally Posted by kluchetta View Post
Extra Credit!!!

Post the equation for the same parabola but is "upside down" to the one I found the equation to!

its the negative of the equation so it would be -(x-2)(x-4)= -(x^2-4x-2x+8)= -x^2+6x-8
post #16 of 20
Thread Starter 
Quote:
Originally Posted by algebrapro18 View Post
its the negative of the equation so it would be -(x-2)(x-4)= -(x^2-4x-2x+8)= -x^2+6x-8
Very good. You get extra credit!
post #17 of 20
Man I wish all mathematics was this easy...tell your daughter to enjoy it while it lasts.
post #18 of 20
post #19 of 20
Quote:
Originally Posted by CarolPetunia View Post
I am SO an English major!
altho i'm not an English major, i AM a communication [so to speak] major! [like the majority of teachers, btw]
post #20 of 20
Quote:
Originally Posted by CarolPetunia View Post
I am SO an English major!
I'll take biology or chemistry over advanced math any day! And by advanced I mean anything above adding, multiplying, dividing using all numbers, no letters included!
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