# Find expressions for the quadratic functions

• Jan 31st 2009, 05:40 PM
question111
Find expressions for the quadratic functions
Find expressions for the quadratic functions whose graphs are shown:

http://img204.imageshack.us/img204/8...aticqv3.th.png
• Jan 31st 2009, 05:44 PM
Jhevon
Quote:

Originally Posted by question111
Find expressions for the quadratic functions whose graphs are shown:

http://img204.imageshack.us/img204/8...aticqv3.th.png

there are several ways to approach this. here's one

note that the vertex is on the x-axis, that is, we have a double root for the vertex

thus, our quadratic is of the form \$\displaystyle y = a(x - 3)^2\$

we are given that the point (4,2) is on the graph, we can use this to find \$\displaystyle a\$, by plugging in \$\displaystyle x = 4\$ and \$\displaystyle y = 2\$ into the form above

• Jan 31st 2009, 05:50 PM
Shyam
Quote:

Originally Posted by question111
Find expressions for the quadratic functions whose graphs are shown:

http://img204.imageshack.us/img204/8...aticqv3.th.png

Your image is so small that it is very hard to see the co-ordinate of vertex and a point in parabola. Please write these coordinates, then it will be solved.
• Jan 31st 2009, 05:51 PM
Jhevon
Quote:

Originally Posted by Shyam
Your image is so small that it is very hard to see the co-ordinate of vertex and a point in parabola. Please write these coordinates, then it will be solved.

if you click on the image, it takes you to a larger one
• Feb 1st 2009, 02:38 PM
question111
So a would be 2, and when I plug that in, I am finally getting a graph like it's shown in the book.

Thank you very much.
• Feb 1st 2009, 03:11 PM
Jhevon
Quote:

Originally Posted by question111
So a would be 2, and when I plug that in, I am finally getting a graph like it's shown in the book.

Thank you very much.

• Jan 24th 2010, 10:48 PM
lovegreen
and so what is your expression
(Thinking)
• Jan 24th 2010, 10:54 PM
Jhevon
Quote:

Originally Posted by lovegreen
(Thinking)

i do not understand your question. we found that a = 2. just plug that into the expression given in post #2 to get the quadratic
• Jan 25th 2010, 12:32 AM
lovegreen
Thanks!
I see it is y = 2(x squared) -12x + 18
• Jan 25th 2010, 03:43 AM
HallsofIvy
Quote:

Originally Posted by lovegreen
I see it is y = 2(x squared) -12x + 18

Why not just leave it as \$\displaystyle y= 2(x- 3)^2\$?