SOLUTION: write an equation in standard form of the parabola that has the same shape as the graph of {{{f(x)=-7x^2}}}, but which has a maximum of {{{9}}} at {{{x=3}}}.

Algebra ->  Algebra  -> Quadratic-relations-and-conic-sections -> SOLUTION: write an equation in standard form of the parabola that has the same shape as the graph of {{{f(x)=-7x^2}}}, but which has a maximum of {{{9}}} at {{{x=3}}}.      Log On

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Question 237370: write an equation in standard form of the parabola that has the same shape as the graph of f%28x%29=-7x%5E2, but which has a maximum of 9 at x=3.
Answer by Edwin McCravy(6941) About Me  (Show Source):
You can put this solution on YOUR website!

First let's draw the graph of the first equation:

drawing%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C%0D%0A%0D%0Agraph%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C-7x%5E2%29+%29

Notice that since its vertex is %27%280%2C0%29%27 it has a maximum
of 0 at x=0.  Now let's plot the point %27%283%2C9%29%27.

drawing%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C%0D%0A%0D%0Agraph%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C-7x%5E2%29%2C%0D%0A%0D%0Aline%283%2B.1%2C9%2C3-.1%2C9%29%2C+line%283%2C9%2B.1%2C3%2C9-.1%29%2Cline%283%2B.1%2C9%2B.1%2C3-.1%2C9-.1%29%2Cline%283%2B.1%2C9-.1%2C3-.1%2C9%2B.1%29+%0D%0A%29

We now need to shift the graph of f%28x%29=-7x%5E2 so that its
vertex %27%280%2C0%29%27 shifts to the point %27%283%2C9%29%27%7D%7D%29.%0D%0A%0D%0AThat+will+take+two+shifts%2C+one+horizontally+to+the+right+3+units%2C+and%0D%0Aanother+vertically+upward+9+units.+We+will+call+the+first+shifted%0D%0Afunction+%7B%7B%7Bg%28x%29 and the second shifted function h%28x%29.

We first shift the graph horizontally 3 units to the right.
This is done by replacing x in the right side of f%28x%29 by 
%28x-3%29, getting g%28x%29=-7%28x-3%29%5E2. 

drawing%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C%0D%0A%0D%0Agraph%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C-7x%5E2%29%2C%0D%0Agraph%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C-7%28x-3%29%5E2%29%2C%0D%0Aline%283%2B.1%2C9%2C3-.1%2C9%29%2C+line%283%2C9%2B.1%2C3%2C9-.1%29%2Cline%283%2B.1%2C9%2B.1%2C3-.1%2C9-.1%29%2Cline%283%2B.1%2C9-.1%2C3-.1%2C9%2B.1%29+%0D%0A%29

But now that graph must be shifted vertically upward by 9 units.
This is done by adding 9 to the right side of g%28x%29,
getting h%28x%29=-7%28x-3%29%5E2%2B9.  Now we draw that graph, and get

drawing%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C%0D%0A%0D%0Agraph%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C-7x%5E2%29%2C%0D%0Agraph%28177.8%2C400%2C-2%2C6%2C-8%2C10%2C%28-7%28x-3%29%5E2%2B9%29%28sqrt%28x-1.93%29%2Fsqrt%28x-1.93%29%29%28sqrt%284.07-x%29%2Fsqrt%284.07-x%29%29%29%2C%0D%0Aline%283%2B.1%2C9%2C3-.1%2C9%29%2C+line%283%2C9%2B.1%2C3%2C9-.1%29%2Cline%283%2B.1%2C9%2B.1%2C3-.1%2C9-.1%29%2Cline%283%2B.1%2C9-.1%2C3-.1%2C9%2B.1%29+%0D%0A%29

So the answer is h%28x%29=-7%28x-3%29%5E2%2B9}.  Notice that it has the
same shape as the original graph of f%28x%29=-7x%5E2.

Edwin