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D( x )
x+4 = 0
7*x+28 = 0
x+4 = 0
x+4 = 0
x+4 = 0 // - 4
x = -4
7*x+28 = 0
7*x+28 = 0
7*x+28 = 0 // - 28
7*x = -28 // : 7
x = -28/7
x = -4
x in (-oo:-4) U (-4:+oo)
1/(7*x+28) = 3/(x+4)-(4/7) // - 3/(x+4)-(4/7)
1/(7*x+28)-(3/(x+4))+4/7 = 0
1/(7*x+28)-3*(x+4)^-1+4/7 = 0
1/(7*x+28)-3/(x+4)+4/7 = 0
(1*7*(x+4))/(7*(7*x+28)*(x+4))+(-3*7*(7*x+28))/(7*(7*x+28)*(x+4))+(4*(7*x+28)*(x+4))/(7*(7*x+28)*(x+4)) = 0
1*7*(x+4)-3*7*(7*x+28)+4*(7*x+28)*(x+4) = 0
28*x^2-140*x+224*x-560+448 = 0
28*x^2+84*x-112 = 0
28*x^2+84*x-112 = 0
28*(x^2+3*x-4) = 0
x^2+3*x-4 = 0
DELTA = 3^2-(-4*1*4)
DELTA = 25
DELTA > 0
x = (25^(1/2)-3)/(1*2) or x = (-25^(1/2)-3)/(1*2)
x = 1 or x = -4
28*(x+4)*(x-1) = 0
(28*(x+4)*(x-1))/(7*(7*x+28)*(x+4)) = 0
(28*(x+4)*(x-1))/(7*(7*x+28)*(x+4)) = 0 // * 7*(7*x+28)*(x+4)
28*(x+4)*(x-1) = 0
( x+4 )
x+4 = 0 // - 4
x = -4
( x-1 )
x-1 = 0 // + 1
x = 1
x in { -4}
x = 1
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