y^2-21y-4=0

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Solution for y^2-21y-4=0 equation: 



y^2-21y-4=0

a = 1; b = -21; c = -4;
Δ = b2-4ac
Δ = -212-4·1·(-4)
Δ = 457
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-\sqrt{457}}{2*1}=\frac{21-\sqrt{457}}{2}
$


$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+\sqrt{457}}{2*1}=\frac{21+\sqrt{457}}{2}
$

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