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D( x )
4*x^2-28 = 0
4*x^2-28 = 0
4*x^2-28 = 0
4*x^2 = 28 // : 4
x^2 = 7
x^2 = 7 // ^ 1/2
abs(x) = 7^(1/2)
x = 7^(1/2) or x = -7^(1/2)
x in (-oo:-7^(1/2)) U (-7^(1/2):7^(1/2)) U (7^(1/2):+oo)
(x^2-(56*x)+8^3-7)/(4*x^2-28) = 0
(x^2-56*x+8^3-7)/(4*x^2-28) = 0
(x^2-56*x+505)/(4*x^2-28) = 0
x^2-56*x+505 = 0
x^2-56*x+505 = 0
DELTA = (-56)^2-(1*4*505)
DELTA = 1116
DELTA > 0
x = (1116^(1/2)+56)/(1*2) or x = (56-1116^(1/2))/(1*2)
x = (6*31^(1/2)+56)/2 or x = (56-6*31^(1/2))/2
(x-((56-6*31^(1/2))/2))*(x-((6*31^(1/2)+56)/2)) = 0
((x-((56-6*31^(1/2))/2))*(x-((6*31^(1/2)+56)/2)))/(4*x^2-28) = 0
( x-((56-6*31^(1/2))/2) )
x-((56-6*31^(1/2))/2) = 0 // + (56-6*31^(1/2))/2
x = (56-6*31^(1/2))/2
( x-((6*31^(1/2)+56)/2) )
x-((6*31^(1/2)+56)/2) = 0 // + (6*31^(1/2)+56)/2
x = (6*31^(1/2)+56)/2
x in { (56-6*31^(1/2))/2, (6*31^(1/2)+56)/2 }
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