# Writing an Equation.

• Jul 30th 2008, 10:16 AM
JoeF107
Writing an Equation.
Question:

Write a Determine the values of b and c such that f(x) = x^2 + bx + c passes through the points (-4,0) and (3,14)

I'm not sure how to approach the problem. I have tried using vertex version of quadratic formula a(x-h)^2+k, but the problem does not specify which ordered pair is the vertex. I also tried plugging into the ordered pairs into my graphing calc, and got an error because I need three ordered pairs for it to give me an expression.

Suggestions?
• Jul 30th 2008, 11:05 AM
flyingsquirrel
Hi
Quote:

Originally Posted by JoeF107
Question:

Write a Determine the values of b and c such that f(x) = x^2 + bx + c passes through the points (-4,0) and (3,14) [...]

Suggestions?

We know that the curve passes through \$\displaystyle (-4,0)\$ and \$\displaystyle (3,14)\$ which means that \$\displaystyle f(-4)=0\$ and that \$\displaystyle f(3)=14\$. Using these two equalities, can you find the value of \$\displaystyle b\$ and \$\displaystyle c\$ ?
• Jul 30th 2008, 12:01 PM
JoeF107
Quote:

Originally Posted by flyingsquirrel
Hi

We know that the curve passes through \$\displaystyle (-4,0)\$ and \$\displaystyle (3,14)\$ which means that \$\displaystyle f(-4)=0\$ and that \$\displaystyle f(3)=14\$. Using these two equalities, can you find the value of \$\displaystyle b\$ and \$\displaystyle c\$ ?

ah, I was over thinking the problem. thanks :)
• Jul 31st 2008, 06:38 AM
tutor
16-4b+c=3
9+3b+c=14

subtracting above equations

-7b=-18
b=18/7

substitute b=18/7 in -4b+c=-13
then c=-19/7