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X2-21X-80=0
We add all the numbers together, and all the variables
X^2-21X-80=0
a = 1; b = -21; c = -80;
Δ = b2-4ac
Δ = -212-4·1·(-80)
Δ = 761
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}$$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}$$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-21)-\sqrt{761}}{2*1}=\frac{21-\sqrt{761}}{2} $$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-21)+\sqrt{761}}{2*1}=\frac{21+\sqrt{761}}{2} $
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