10=4.9*a^2

Solution for 10=4.9*a^2 equation:

10=4.9a^2

We move all terms to the left:

10-(4.9a^2)=0

We get rid of parentheses

-4.9a^2+10=0

a = -4.9; b = 0; c = +10;
Δ = b2-4ac
Δ = 02-4·(-4.9)·10
Δ = 196
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{196}=14$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-14}{2*-4.9}=\frac{-14}{-9.8}
=1+3.5/8.1666666666667
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+14}{2*-4.9}=\frac{14}{-9.8}
=-1+3.5/8.1666666666667
$