Y=-1.25x^2+15

Solution for Y=-1.25x^2+15 equation:

=-1.25Y^2+15

We move all terms to the left:

-(-1.25Y^2+15)=0

We get rid of parentheses

1.25Y^2-15=0

a = 1.25; b = 0; c = -15;
Δ = b2-4ac
Δ = 02-4·1.25·(-15)
Δ = 75
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{75}=\sqrt{25*3}=\sqrt{25}*\sqrt{3}=5\sqrt{3}$
$Y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-5\sqrt{3}}{2*1.25}=\frac{0-5\sqrt{3}}{2.5}
=-\frac{5\sqrt{3}}{2.5}
$
$Y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+5\sqrt{3}}{2*1.25}=\frac{0+5\sqrt{3}}{2.5}
=\frac{5\sqrt{3}}{2.5}
$