Question 1195875
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Finding the equation using standard form {{{y=ax^2+bx+c}}} and using the three known points to form a system of three equations in a, b, and c is one way to get the answer.<br>
Usually an easier way, when the vertex of the parabola is known, is to use the vertex form of the equation of a parabola:<br>
{{{y-k=a(x-h)^2}}}<br>
Knowing the points (0,0), (60,20), and (120,0), we know the vertex is (60,20).  So<br>
{{{y-20=a(x-60)^2}}}<br>
Use either of the other two points to determine the constant a.  Using (0,0)...<br>
{{{0-20=a(0-60)^2}}}
{{{-20=a(3600)}}}
{{{a=-20/3600=-1/180}}}<br>
ANSWER: {{{y-20=(-1/180)(x-60)^2}}}<br>
Then manipulate that equation to put it in the required form, if necessary.<br>