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D( k )
42-(7*k) = 0
42-(7*k) = 0
42-(7*k) = 0
42-7*k = 0
42-7*k = 0 // - 42
-7*k = -42 // : -7
k = -42/(-7)
k = 6
k in (-oo:6) U (6:+oo)
3*k-(18/(42-(7*k))) = 0
3*k-18*(42-7*k)^-1 = 0
3*k-18/(42-7*k) = 0
(3*k*(42-7*k))/(42-7*k)-18/(42-7*k) = 0
3*k*(42-7*k)-18 = 0
126*k-21*k^2-18 = 0
126*k-21*k^2-18 = 0
3*(42*k-7*k^2-6) = 0
42*k-7*k^2-6 = 0
DELTA = 42^2-(-7*(-6)*4)
DELTA = 1596
DELTA > 0
k = (1596^(1/2)-42)/(-7*2) or k = (-1596^(1/2)-42)/(-7*2)
k = (2*399^(1/2)-42)/(-14) or k = (-2*399^(1/2)-42)/(-14)
3*(k-((2*399^(1/2)-42)/(-14)))*(k-((-2*399^(1/2)-42)/(-14))) = 0
(3*(k-((2*399^(1/2)-42)/(-14)))*(k-((-2*399^(1/2)-42)/(-14))))/(42-7*k) = 0
(3*(k-((2*399^(1/2)-42)/(-14)))*(k-((-2*399^(1/2)-42)/(-14))))/(42-7*k) = 0 // * 42-7*k
3*(k-((2*399^(1/2)-42)/(-14)))*(k-((-2*399^(1/2)-42)/(-14))) = 0
( 3 )
3 = 0
k belongs to the empty set
( k-((-2*399^(1/2)-42)/(-14)) )
k-((-2*399^(1/2)-42)/(-14)) = 0 // + (-2*399^(1/2)-42)/(-14)
k = (-2*399^(1/2)-42)/(-14)
( k-((2*399^(1/2)-42)/(-14)) )
k-((2*399^(1/2)-42)/(-14)) = 0 // + (2*399^(1/2)-42)/(-14)
k = (2*399^(1/2)-42)/(-14)
k in { (-2*399^(1/2)-42)/(-14), (2*399^(1/2)-42)/(-14) }
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