a*(9-2a)=4

Solution for a*(9-2a)=4 equation:

a(9-2a)=4

We move all terms to the left:

a(9-2a)-(4)=0

We add all the numbers together, and all the variables

a(-2a+9)-4=0

We multiply parentheses

-2a^2+9a-4=0

a = -2; b = 9; c = -4;
Δ = b2-4ac
Δ = 92-4·(-2)·(-4)
Δ = 49
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{49}=7$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(9)-7}{2*-2}=\frac{-16}{-4}
=+4
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(9)+7}{2*-2}=\frac{-2}{-4}
=1/2
$