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D( x )
3*x^3 = 0
3*x^3 = 0
3*x^3 = 0
3*x^3 = 0 // : 3
x^3 = 0
x = 0
x in (-oo:0) U (0:+oo)
(12*x^6-(9*x^4))/(3*x^3) = 0
(12*x^6-9*x^4)/(3*x^3) = 0
12*x^6-9*x^4 = 0
3*x^4*(4*x^2-3) = 0
4*x^2 = 3 // : 4
x^2 = 3/4
x^2 = 3/4 // ^ 1/2
abs(x) = (3/4)^(1/2)
x = (3/4)^(1/2) or x = -(3/4)^(1/2)
3*x^4*(x-(3/4)^(1/2))*(x+(3/4)^(1/2)) = 0
(3*x^4*(x-(3/4)^(1/2))*(x+(3/4)^(1/2)))/(3*x^3) = 0
( 3*x^4 )
3*x^4 = 0 // : 3
x^4 = 0
x = 0
( x+(3/4)^(1/2) )
x+(3/4)^(1/2) = 0 // - (3/4)^(1/2)
x = -(3/4)^(1/2)
( x-(3/4)^(1/2) )
x-(3/4)^(1/2) = 0 // + (3/4)^(1/2)
x = (3/4)^(1/2)
x in { 0}
x in { -(3/4)^(1/2), (3/4)^(1/2) }
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