-.7t^2+42t-315=0

Solution for -.7t^2+42t-315=0 equation:

-.7t^2+42t-315=0

We add all the numbers together, and all the variables

-0.7t^2+42t-315=0

a = -0.7; b = 42; c = -315;
Δ = b2-4ac
Δ = 422-4·(-0.7)·(-315)
Δ = 882
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:

$\sqrt{\Delta}=\sqrt{882}=\sqrt{441*2}=\sqrt{441}*\sqrt{2}=21\sqrt{2}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(42)-21\sqrt{2}}{2*-0.7}=\frac{-42-21\sqrt{2}}{-1.4}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(42)+21\sqrt{2}}{2*-0.7}=\frac{-42+21\sqrt{2}}{-1.4}
$