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X2-2x-21=0

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Solution for X2-2x-21=0 equation: 



X2-2X-21=0

We add all the numbers together, and all the variables

X^2-2X-21=0

a = 1; b = -2; c = -21;
Δ = b2-4ac
Δ = -22-4·1·(-21)
Δ = 88
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}

The end solution:


\sqrt{\Delta}=\sqrt{88}=\sqrt{4*22}=\sqrt{4}*\sqrt{22}=2\sqrt{22}


X_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-2)-2\sqrt{22}}{2*1}=\frac{2-2\sqrt{22}}{2}



X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2)+2\sqrt{22}}{2*1}=\frac{2+2\sqrt{22}}{2}

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