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D( x )
x^2-9 = 0
x^2-9 = 0
x^2-9 = 0
1*x^2 = 9 // : 1
x^2 = 9
x^2 = 9 // ^ 1/2
abs(x) = 3
x = 3 or x = -3
x in (-oo:-3) U (-3:3) U (3:+oo)
3 = (40*x)/(x^2-9) // - (40*x)/(x^2-9)
3-((40*x)/(x^2-9)) = 0
3-40*x*(x^2-9)^-1 = 0
(-40*x)/(x^2-9)+3 = 0
(-40*x)/(x^2-9)+(3*(x^2-9))/(x^2-9) = 0
3*(x^2-9)-40*x = 0
3*x^2-40*x-27 = 0
3*x^2-40*x-27 = 0
3*x^2-40*x-27 = 0
DELTA = (-40)^2-(-27*3*4)
DELTA = 1924
DELTA > 0
x = (1924^(1/2)+40)/(2*3) or x = (40-1924^(1/2))/(2*3)
x = (2*481^(1/2)+40)/6 or x = (40-2*481^(1/2))/6
(x-((40-2*481^(1/2))/6))*(x-((2*481^(1/2)+40)/6)) = 0
((x-((40-2*481^(1/2))/6))*(x-((2*481^(1/2)+40)/6)))/(x^2-9) = 0
((x-((40-2*481^(1/2))/6))*(x-((2*481^(1/2)+40)/6)))/(x^2-9) = 0 // * x^2-9
(x-((40-2*481^(1/2))/6))*(x-((2*481^(1/2)+40)/6)) = 0
( x-((2*481^(1/2)+40)/6) )
x-((2*481^(1/2)+40)/6) = 0 // + (2*481^(1/2)+40)/6
x = (2*481^(1/2)+40)/6
( x-((40-2*481^(1/2))/6) )
x-((40-2*481^(1/2))/6) = 0 // + (40-2*481^(1/2))/6
x = (40-2*481^(1/2))/6
x in { (2*481^(1/2)+40)/6, (40-2*481^(1/2))/6 }
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