# Thread: Parabola question???

1. ## Parabola question???

My question is kind of basic and stupid... but how in the world do you graph THIS question??
I need someone to walk me through it.

y = x^2 - 3x - 4

Should i factorise it or what?? It seems like iI should know this question but i don't.

2. ## Re: Parabola question???

Factorisation gives y=(x-4)(x+1), thus the roots are x=-1 and x=4. Further the minimum is attained at x=3/2 (half way between the roots) and y(3/2) = -25/4. Now draw a nice parabola through (-1,0) , (3/2,-25/4) and (4,0).

3. ## Re: Parabola question???

Yep that looks right to me. If you have a basic calculator you can put it into table mode, and input the equation. It then gives you the results for any input of $x$.

However, it is easy to calculte without a calculator. Just get take values for $x$, say -5, 0, 5, and stick them into the equation. Work it out, and you will obtain a table of results.

ie.
$y=x^2-3x-4$

Take $x=0$

then, $y=0^2-(3\times0)-4$
Therefore, $y=-4$

Do the same for the other values, and then you can plot them.

4. ## Re: Parabola question???

hi would I do something similar to solve equations such as

y=-3x+2

and

y=2x^2-7x-4

dave

5. ## Re: Parabola question???

Then start your own thread. Do not "hijack" someone else's thread to ask separate questions.

6. ## Re: Parabola question???

sorry, I`ll do it now