Question 553590
The x-coordinate of the vertex is at 
{{{ x = -b/(2a) }}} where the equation 
has the form {{{ f(x) = ax^2 + b*x + c }}}|
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{{{ f(x) = (-3/10)*x^2 + (9/2)*x - 7/6 }}}
{{{ a = -3/10 }}}
{{{ b = 9/2 }}}
{{{ -b/(2a) = -(9/2)/(2*(-3/10)) }}}
{{{ -b/(2a) = (-10/6)*(-9/2) }}}
{{{ -b/(2a) = 90/12 }}}
{{{ -b/(2a) = 15/2 }}}
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So far, the vertex is at ( 15/2,y )
Now find the y-coordinate
{{{ f( 15/2 ) = (-3/10)*(15/2)^2 + (9/2)*(15/2) - 7/6 }}}
{{{ f( 15/2 ) = (-3/10)*(225/4) + 135/4 - 7/6 }}}
{{{ f( 15/2 ) = -675/40 + 540/40 - 7/6 }}}
{{{ f(15/2) = -2025/120 + 1620/120 - 140/120 }}}
{{{ f(15/2) = -545/120 }}}
{{{ f(15/2) = -109/24 }}}
The vertex is at (15/2, -109/24)
Unless I made a mistake