-4.9x^2-7.1x=-8

Solution for -4.9x^2-7.1x=-8 equation:

-4.9x^2-7.1x=-8

We move all terms to the left:

-4.9x^2-7.1x-(-8)=0

We add all the numbers together, and all the variables

-4.9x^2-7.1x+8=0

a = -4.9; b = -7.1; c = +8;
Δ = b2-4ac
Δ = -7.12-4·(-4.9)·8
Δ = 207.21
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{-(-7.1)-\sqrt{207.21}}{2*-4.9}=\frac{7.1-\sqrt{207.21}}{-9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7.1)+\sqrt{207.21}}{2*-4.9}=\frac{7.1+\sqrt{207.21}}{-9.8}
$