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D( x )
x-7 = 0
x-7 = 0
x-7 = 0
x-7 = 0 // + 7
x = 7
x in (-oo:7) U (7:+oo)
(x^2-(3*x)-21)/(x-7) = 0
(x^2-3*x-21)/(x-7) = 0
x^2-3*x-21 = 0
x^2-3*x-21 = 0
DELTA = (-3)^2-(-21*1*4)
DELTA = 93
DELTA > 0
x = (93^(1/2)+3)/(1*2) or x = (3-93^(1/2))/(1*2)
x = (93^(1/2)+3)/2 or x = (3-93^(1/2))/2
(x-((3-93^(1/2))/2))*(x-((93^(1/2)+3)/2)) = 0
((x-((3-93^(1/2))/2))*(x-((93^(1/2)+3)/2)))/(x-7) = 0
( x-((3-93^(1/2))/2) )
x-((3-93^(1/2))/2) = 0 // + (3-93^(1/2))/2
x = (3-93^(1/2))/2
( x-((93^(1/2)+3)/2) )
x-((93^(1/2)+3)/2) = 0 // + (93^(1/2)+3)/2
x = (93^(1/2)+3)/2
x in { (3-93^(1/2))/2, (93^(1/2)+3)/2 }
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