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Mathematics 17 Online
OpenStudy (angelax0):

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OpenStudy (eliesaab):

Let \[ x=g(y)=a y^2 + b y + c \] We need to find a,b,c. We need to find three equations in three unknowns (a,b,c) and solve them and we will be done

OpenStudy (eliesaab):

It seems that we only have two informations, but in fact we have three

OpenStudy (eliesaab):

The point (4,-2) is a point on the parabola and its vertex at the same time. (2 equations from here) Also the point (3,4) is on the parabola. (one equation form here) So we are all set

OpenStudy (eliesaab):

Interpreting the words into equations gives \[ g'(-2)= b-4 a=0 \\ g(-2)=4 a-2 b+c=4 \\ g(4)= 16 a+4 b+c=3 \\ \]

OpenStudy (eliesaab):

Solving them, you get \[ \left( \begin{array}{ccc} a=-\frac{1}{36} ,& b=-\frac{1}{9}, & c=\frac{35}{9} \\ \end{array} \right) \]

OpenStudy (eliesaab):

Finally, the equation of the parabola is \[ x=-\frac{y^2}{36}-\frac{y}{9}+\frac{35}{9} \]

OpenStudy (eliesaab):

Are you with me?

OpenStudy (eliesaab):

OpenStudy (eliesaab):

The above is the graph. You can see the two points on it and one of them is the vertex.

OpenStudy (eliesaab):

You can also notice that your parabola intersects the y-axis at y=-14 and y=10

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