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D( x )
x = 0
3*x+18 = 0
x = 0
x = 0
3*x+18 = 0
3*x+18 = 0
3*x+18 = 0 // - 18
3*x = -18 // : 3
x = -18/3
x = -6
x in (-oo:-6) U (-6:0) U (0:+oo)
1/x = x/(3*x+18) // - x/(3*x+18)
1/x-(x/(3*x+18)) = 0
(-1*x)/(3*x+18)+1/x = 0
(-1*x^2)/(x*(3*x+18))+(1*(3*x+18))/(x*(3*x+18)) = 0
1*(3*x+18)-1*x^2 = 0
3*x-x^2+18 = 0
3*x-x^2+18 = 0
3*x-x^2+18 = 0
DELTA = 3^2-(-1*4*18)
DELTA = 81
DELTA > 0
x = (81^(1/2)-3)/(-1*2) or x = (-81^(1/2)-3)/(-1*2)
x = -3 or x = 6
(x+3)*(x-6) = 0
((x+3)*(x-6))/(x*(3*x+18)) = 0
((x+3)*(x-6))/(x*(3*x+18)) = 0 // * x*(3*x+18)
(x+3)*(x-6) = 0
( x+3 )
x+3 = 0 // - 3
x = -3
( x-6 )
x-6 = 0 // + 6
x = 6
x in { -3, 6 }
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