75=4.9x^2

Solution for 75=4.9x^2 equation:

75=4.9x^2

We move all terms to the left:

75-(4.9x^2)=0

We get rid of parentheses

-4.9x^2+75=0

a = -4.9; b = 0; c = +75;
Δ = b2-4ac
Δ = 02-4·(-4.9)·75
Δ = 1470
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1470}=\sqrt{49*30}=\sqrt{49}*\sqrt{30}=7\sqrt{30}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-7\sqrt{30}}{2*-4.9}=\frac{0-7\sqrt{30}}{-9.8}
=-\frac{7\sqrt{30}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+7\sqrt{30}}{2*-4.9}=\frac{0+7\sqrt{30}}{-9.8}
=\frac{7\sqrt{30}}{-9.8}
$