3a+4-a(a=3)

Solution for 3a+4-a(a=3) equation:

3a+4-a(a=3)

We move all terms to the left:

3a+4-a(a-(3))=0

We multiply parentheses

-a^2+3a+3a+4=0

We add all the numbers together, and all the variables

-1a^2+6a+4=0

a = -1; b = 6; c = +4;
Δ = b2-4ac
Δ = 62-4·(-1)·4
Δ = 52
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{52}=\sqrt{4*13}=\sqrt{4}*\sqrt{13}=2\sqrt{13}$
$a_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(6)-2\sqrt{13}}{2*-1}=\frac{-6-2\sqrt{13}}{-2}
$
$a_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(6)+2\sqrt{13}}{2*-1}=\frac{-6+2\sqrt{13}}{-2}
$