4.9t^2+20t=15

Solution for 4.9t^2+20t=15 equation:

4.9t^2+20t=15

We move all terms to the left:

4.9t^2+20t-(15)=0

a = 4.9; b = 20; c = -15;
Δ = b2-4ac
Δ = 202-4·4.9·(-15)
Δ = 694
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-\sqrt{694}}{2*4.9}=\frac{-20-\sqrt{694}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+\sqrt{694}}{2*4.9}=\frac{-20+\sqrt{694}}{9.8}
$