-4.9x^2-21x+40=0

Solution for -4.9x^2-21x+40=0 equation:

-4.9x^2-21x+40=0

a = -4.9; b = -21; c = +40;
Δ = b2-4ac
Δ = -212-4·(-4.9)·40
Δ = 1225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1225}=35$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-35}{2*-4.9}=\frac{-14}{-9.8}
=1+3.5/8.1666666666667
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+35}{2*-4.9}=\frac{56}{-9.8}
=-5+7/9.8
$