SOLUTION: The graph of a parabola passes through the points (3/2, 4/3) and (0, −6) and has a horizontal tangent line at (3/2, 4/3). Find an equation for the parabola and sketch its graph

Algebra ->  Matrices-and-determiminant -> SOLUTION: The graph of a parabola passes through the points (3/2, 4/3) and (0, −6) and has a horizontal tangent line at (3/2, 4/3). Find an equation for the parabola and sketch its graph      Log On


   



Question 1153918: The graph of a parabola passes through the points (3/2, 4/3) and (0, −6) and
has a horizontal tangent line at (3/2, 4/3). Find an equation for the parabola
and sketch its graph.

Answer by ikleyn(52792) About Me  (Show Source):
You can put this solution on YOUR website!
.

Since the parabola has a horizontal tangent line at the point (3/2,4/3), it means 

that this point (3/2,4/3) is the vertex of the parabola.


Hence, the parabola has the form


    y(x) = a%2A%28x-3%2F2%29%5E2+%2B+4%2F3,


where "a" is a coefficient (real number), now unknown.


To find "a", use the fact that the plot of the parabola passes through the point (0,-6). It means that


    y(0) = -6,   or   a%2A%280+-+3%2F2%29%5E2+%2B+4%2F3 = -6,   or


    a%2A%283%2F2%29%5E2+%2B+4%2F3 = -6.


It gives


    a%2A%289%2F4%29 = -6+-+4%2F3 = %28-18-4%29%2F3 = -22%2F3,


hence


    a = %284%2F9%29%2A%28-22%2F3%29 = -88%2F27.


Thus the equation of the parabola is  


    y(x) = %28-88%2F27%29%2A%28x-3%2F2%29%5E2+%2B+4%2F3.


You can transform it to any other equivalent form you wish.


Regarding the plot, do it on your own.


You may use free of charge plotting tools from the Internet.