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D( x )
x^2-(4*x)-21 = 0
x^2-(4*x)-21 = 0
x^2-(4*x)-21 = 0
x^2-4*x-21 = 0
x^2-4*x-21 = 0
DELTA = (-4)^2-(-21*1*4)
DELTA = 100
DELTA > 0
x = (100^(1/2)+4)/(1*2) or x = (4-100^(1/2))/(1*2)
x = 7 or x = -3
x in (-oo:-3) U (-3:7) U (7:+oo)
(5*x-3)/(x^2-(4*x)-21) = 0
(5*x-3)/(x^2-4*x-21) = 0
x^2-4*x-21 = 0
x^2-4*x-21 = 0
DELTA = (-4)^2-(-21*1*4)
DELTA = 100
DELTA > 0
x = (100^(1/2)+4)/(1*2) or x = (4-100^(1/2))/(1*2)
x = 7 or x = -3
(x+3)*(x-7) = 0
(5*x-3)/((x+3)*(x-7)) = 0
5*x-3 = 0 // + 3
5*x = 3 // : 5
x = 3/5
x = 3/5
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