-9y^2+21y+10=0

Solution for -9y^2+21y+10=0 equation:

-9y^2+21y+10=0

a = -9; b = 21; c = +10;
Δ = b2-4ac
Δ = 212-4·(-9)·10
Δ = 801
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{801}=\sqrt{9*89}=\sqrt{9}*\sqrt{89}=3\sqrt{89}$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-3\sqrt{89}}{2*-9}=\frac{-21-3\sqrt{89}}{-18}
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+3\sqrt{89}}{2*-9}=\frac{-21+3\sqrt{89}}{-18}
$