21x-40=21/x

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Solution for 21x-40=21/x equation: 


D( x )

x = 0

x = 0

x = 0

x in (-oo:0) U (0:+oo)

21*x-40 = 21/x // - 21/x

21*x-(21/x)-40 = 0

21*x-21*x^-1-40 = 0

21*x^1-21*x^-1-40*x^0 = 0

(21*x^2-40*x^1-21*x^0)/(x^1) = 0 // * x^2

x^1*(21*x^2-40*x^1-21*x^0) = 0

x^1

21*x^2-40*x-21 = 0

21*x^2-40*x-21 = 0

DELTA = (-40)^2-(-21*4*21)

DELTA = 3364

DELTA > 0

x = (3364^(1/2)+40)/(2*21) or x = (40-3364^(1/2))/(2*21)

x = 7/3 or x = -3/7

x in { -3/7, 7/3} 

x in { -3/7, 7/3 }

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