4y^2-81y+315=0

Solution for 4y^2-81y+315=0 equation:

4y^2-81y+315=0

a = 4; b = -81; c = +315;
Δ = b2-4ac
Δ = -812-4·4·315
Δ = 1521
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{1521}=39$
$y_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-81)-39}{2*4}=\frac{42}{8}
=5+1/4
$
$y_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-81)+39}{2*4}=\frac{120}{8}
=15
$