# Thread: Writing an Equation.

1. ## 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?

2. Hi
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 $\displaystyle c$ ?

3. 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

4. 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