9x^2=21x-8=0

Solution for 9x^2=21x-8=0 equation:

9x^2=21x-8=0

We move all terms to the left:

9x^2-(21x-8)=0

We get rid of parentheses

9x^2-21x+8=0

a = 9; b = -21; c = +8;
Δ = b2-4ac
Δ = -212-4·9·8
Δ = 153
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{153}=\sqrt{9*17}=\sqrt{9}*\sqrt{17}=3\sqrt{17}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-3\sqrt{17}}{2*9}=\frac{21-3\sqrt{17}}{18}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+3\sqrt{17}}{2*9}=\frac{21+3\sqrt{17}}{18}
$