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X2-2X-15=0X=-3
We move all terms to the left:
X2-2X-15-(0X)=0
We add all the numbers together, and all the variables
X^2-3X-15=0
a = 1; b = -3; c = -15;
Δ = b2-4ac
Δ = -32-4·1·(-15)
Δ = 69
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{-(-3)-\sqrt{69}}{2*1}=\frac{3-\sqrt{69}}{2} $$X_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-3)+\sqrt{69}}{2*1}=\frac{3+\sqrt{69}}{2} $
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