700=4.9*t2

Solution for 700=4.9*t2 equation:

700=4.9*t2

We move all terms to the left:

700-(4.9*t2)=0

We add all the numbers together, and all the variables

-(+4.9t^2)+700=0

We get rid of parentheses

-4.9t^2+700=0

a = -4.9; b = 0; c = +700;
Δ = b2-4ac
Δ = 02-4·(-4.9)·700
Δ = 13720
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{13720}=\sqrt{4*3430}=\sqrt{4}*\sqrt{3430}=2\sqrt{3430}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(0)-2\sqrt{3430}}{2*-4.9}=\frac{0-2\sqrt{3430}}{-9.8}
=-\frac{2\sqrt{3430}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(0)+2\sqrt{3430}}{2*-4.9}=\frac{0+2\sqrt{3430}}{-9.8}
=\frac{2\sqrt{3430}}{-9.8}
$