Y=-0.0045x^2+0.8x+15

Solution for Y=-0.0045x^2+0.8x+15 equation:

=-0.0045Y^2+0.8Y+15

We move all terms to the left:

-(-0.0045Y^2+0.8Y+15)=0

We get rid of parentheses

0.0045Y^2-0.8Y-15=0

a = 0.0045; b = -0.8; c = -15;
Δ = b2-4ac
Δ = -0.82-4·0.0045·(-15)
Δ = 0.91
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-0.8)-\sqrt{0.91}}{2*0.0045}=\frac{0.8-\sqrt{0.91}}{0.009}
$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.8)+\sqrt{0.91}}{2*0.0045}=\frac{0.8+\sqrt{0.91}}{0.009}
$