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D( y )
3*y^4 = 0
3*y^4 = 0
3*y^4 = 0
3*y^4 = 0 // : 3
y^4 = 0
y = 0
y in (-oo:0) U (0:+oo)
(21*y^5-(5*y^4)-(18*y^3))/(3*y^4) = 0
(21*y^5-5*y^4-18*y^3)/(3*y^4) = 0
21*y^5-5*y^4-18*y^3 = 0
y^3*(21*y^2-5*y-18) = 0
21*y^2-5*y-18 = 0
DELTA = (-5)^2-(-18*4*21)
DELTA = 1537
DELTA > 0
y = (1537^(1/2)+5)/(2*21) or y = (5-1537^(1/2))/(2*21)
y = (1537^(1/2)+5)/42 or y = (5-1537^(1/2))/42
y^3*(y-((5-1537^(1/2))/42))*(y-((1537^(1/2)+5)/42)) = 0
(y^3*(y-((5-1537^(1/2))/42))*(y-((1537^(1/2)+5)/42)))/(3*y^4) = 0
( y-((1537^(1/2)+5)/42) )
y-((1537^(1/2)+5)/42) = 0 // + (1537^(1/2)+5)/42
y = (1537^(1/2)+5)/42
( y-((5-1537^(1/2))/42) )
y-((5-1537^(1/2))/42) = 0 // + (5-1537^(1/2))/42
y = (5-1537^(1/2))/42
( y^3 )
1*y^3 = 0 // : 1
y^3 = 0
y = 0
y in { 0}
y in { (1537^(1/2)+5)/42, (5-1537^(1/2))/42 }
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