700=4.9x^2+8x

Solution for 700=4.9x^2+8x equation:

700=4.9x^2+8x

We move all terms to the left:

700-(4.9x^2+8x)=0

We get rid of parentheses

-4.9x^2-8x+700=0

a = -4.9; b = -8; c = +700;
Δ = b2-4ac
Δ = -82-4·(-4.9)·700
Δ = 13784
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:

$\sqrt{\Delta}=\sqrt{13784}=\sqrt{4*3446}=\sqrt{4}*\sqrt{3446}=2\sqrt{3446}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-2\sqrt{3446}}{2*-4.9}=\frac{8-2\sqrt{3446}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+2\sqrt{3446}}{2*-4.9}=\frac{8+2\sqrt{3446}}{-9.8}
$