(5x+1)(x-1.6)=0

Solution for (5x+1)(x-1.6)=0 equation:

(5x+1)(x-1.6)=0

We multiply parentheses ..

(+5x^2-8x+x-1.6)=0

We get rid of parentheses

5x^2-8x+x-1.6=0

We add all the numbers together, and all the variables

5x^2-7x-1.6=0

a = 5; b = -7; c = -1.6;
Δ = b2-4ac
Δ = -72-4·5·(-1.6)
Δ = 81
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{81}=9$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-7)-9}{2*5}=\frac{-2}{10}
=-1/5
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-7)+9}{2*5}=\frac{16}{10}
=1+3/5
$