-7.5(x-1.5)(x+5)=0

Solution for -7.5(x-1.5)(x+5)=0 equation:

-7.5(x-1.5)(x+5)=0

We multiply parentheses ..

-7.5(+x^2+5x-1.5x-7.5)=0

We multiply parentheses

-7.5x^2-37.5x+7.5x+56.25=0

We add all the numbers together, and all the variables

-7.5x^2-30x+56.25=0

a = -7.5; b = -30; c = +56.25;
Δ = b2-4ac
Δ = -302-4·(-7.5)·56.25
Δ = 2587.5
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{-(-30)-\sqrt{2587.5}}{2*-7.5}=\frac{30-\sqrt{2587.5}}{-15}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+\sqrt{2587.5}}{2*-7.5}=\frac{30+\sqrt{2587.5}}{-15}
$