7=0.25*d^2

Solution for 7=0.25*d^2 equation:

7=0.25d^2

We move all terms to the left:

7-(0.25d^2)=0

We get rid of parentheses

-0.25d^2+7=0

a = -0.25; b = 0; c = +7;
Δ = b2-4ac
Δ = 02-4·(-0.25)·7
Δ = 7
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-\sqrt{7}}{2*-0.25}=\frac{0-\sqrt{7}}{-0.5}
=-\frac{\sqrt{}}{-0.5}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+\sqrt{7}}{2*-0.25}=\frac{0+\sqrt{7}}{-0.5}
=\frac{\sqrt{}}{-0.5}
$