(0.3-x)(0.4-x)=5.1

Solution for (0.3-x)(0.4-x)=5.1 equation:

(0.3-x)(0.4-x)=5.1

We move all terms to the left:

(0.3-x)(0.4-x)-(5.1)=0

We add all the numbers together, and all the variables

(-1x+0.3)(-1x+0.4)-(5.1)=0

We add all the numbers together, and all the variables

(-1x+0.3)(-1x+0.4)-5.1=0

We multiply parentheses ..

(+x^2-0.4x-0.3x+0.12)-5.1=0

We get rid of parentheses

x^2-0.4x-0.3x+0.12-5.1=0

We add all the numbers together, and all the variables

x^2-0.7x-4.98=0

a = 1; b = -0.7; c = -4.98;
Δ = b2-4ac
Δ = -0.72-4·1·(-4.98)
Δ = 20.41
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{-(-0.7)-\sqrt{20.41}}{2*1}=\frac{0.7-\sqrt{20.41}}{2}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-0.7)+\sqrt{20.41}}{2*1}=\frac{0.7+\sqrt{20.41}}{2}
$