0=-0.8x^2+7x-15

Solution for 0=-0.8x^2+7x-15 equation:

0=-0.8x^2+7x-15

We move all terms to the left:

0-(-0.8x^2+7x-15)=0

We add all the numbers together, and all the variables

-(-0.8x^2+7x-15)=0

We get rid of parentheses

0.8x^2-7x+15=0

a = 0.8; b = -7; c = +15;
Δ = b2-4ac
Δ = -72-4·0.8·15
Δ = 1
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1}=1$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-1}{2*0.8}=\frac{6}{1.6}
=3+1/1.3333333333333
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+1}{2*0.8}=\frac{8}{1.6}
=5
$