Math CentralQuandaries & Queries


Question from Salehah, a student:

Hi there, i don't know how to do quadratic equations. So how do i do the question,
that says: x-int -4 and 2, and y-int of 4? and we are to make a quadratic function with this information.

Please help!
Thank you very much!

Hi Salehah,

If a is an x-intercept, then f(a) = 0 and (x-a) is a factor. This is one of the most important things to know about polynomials. Remember it's minus, not plus!

So if 2 and -4 are both x-intercepts, you know two factors, and that's all a quadratic has. So, up to a multiplicative constant , you know the answer. Write it down... and remember that
(x- -4) is the same as (x+4)

Now, what is the y-intercept of your quadratic - that is, f(0)? If it's 4, you're done (but it isn't if you did everything right up till now). So multiply by whatever you need to in order to get the right y-intercept; this won't change the x-intercepts of course.

Good Hunting!

About Math Central


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.
Quandaries & Queries page Home page University of Regina PIMS