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-5+21x-4x^2=0
a = -4; b = 21; c = -5;
Δ = b2-4ac
Δ = 212-4·(-4)·(-5)
Δ = 361
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}$$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$$\sqrt{\Delta}=\sqrt{361}=19$$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-19}{2*-4}=\frac{-40}{-8} =+5 $$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+19}{2*-4}=\frac{-2}{-8} =1/4 $
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