Graphing a Parabola
Date: 3 Apr 1995 18:53:03 -0400 From: Anonymous Subject: quadratic equations Dear Dr. Math, I'm doing my homework and I don't understand how to do this problem, and I was hoping you could show me. How do you graph the quadratic equation, y=3(x+1)^2 - 20? Thanks for your help. your pal, cornfed9 (screen name)
Date: 3 Apr 1995 20:24:35 -0400 From: Dr. Ken Subject: Re: quadratic equations Hello there! When doing this kind of problem, it helps to have an idea what the standard parabola y=x^2 looks like; I'm sure you've seen it. Then you see how your equation differs from the standard, piece by piece. So in your case, let's build up your equation. If it were y = (x+1)^2, it would just be the standard parabola, but moved to the left one unit. Then we multiply by 3, which takes the whole thing and makes it three times as tall and skinny. Then when you subtract 20 to get 3(x+1)^2 - 20, the whole picture moves down 20 units. Then you're done. So this is a parabola centered at (-1, -20), and three times as tall & skinny as the standard parabola. Hope this helps. -Ken "Dr." Math
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