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X2+21X+20=0
We add all the numbers together, and all the variables
X^2+21X+20=0
a = 1; b = 21; c = +20;
Δ = b2-4ac
Δ = 212-4·1·20
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$$X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(21)-19}{2*1}=\frac{-40}{2} =-20 $$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(21)+19}{2*1}=\frac{-2}{2} =-1 $
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