-7x2+.14x+21=0

Solution for -7x2+.14x+21=0 equation:

-7x^2+.14x+21=0

a = -7; b = .14; c = +21;
Δ = b2-4ac
Δ = .142-4·(-7)·21
Δ = 588.0196
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(.14)-\sqrt{588.0196}}{2*-7}=\frac{-0.14-\sqrt{588.0196}}{-14}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(.14)+\sqrt{588.0196}}{2*-7}=\frac{-0.14+\sqrt{588.0196}}{-14}
$