graphing a fuction

[ree]

The function is y =x squared - 9. I do not know how I would graph this. Also, why is it not necessary to plot points to graph when using y = a (x-h)squared +k? Thank you so much for your help! This is really stressing me out!

 

[tkhunny]

It helps a lot if you know what you are graphing. Whether it looks like y = a*x^2 + b*x + c, or y = a*(x-h)^2 + k, it is still a parabola with axis of symmetry parallel to the y-axis, opening up or down according to the sign of 'a'.

The h,k version tells you where to put the vertex. That can be very helpful. If you know about '4p' you can also tell a few other things rather quickly from the h,k version.