-4t+0,68t^2-25=0

Solution for -4t+0,68t^2-25=0 equation:

-4t+0.68t^2-25=0

a = 0.68; b = -4; c = -25;
Δ = b2-4ac
Δ = -42-4·0.68·(-25)
Δ = 84
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:

$\sqrt{\Delta}=\sqrt{84}=\sqrt{4*21}=\sqrt{4}*\sqrt{21}=2\sqrt{21}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-4)-2\sqrt{21}}{2*0.68}=\frac{4-2\sqrt{21}}{1.36}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-4)+2\sqrt{21}}{2*0.68}=\frac{4+2\sqrt{21}}{1.36}
$