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D( x )
5*x+15 = 0
x+3 = 0
5*x+15 = 0
5*x+15 = 0
5*x+15 = 0 // - 15
5*x = -15 // : 5
x = -15/5
x = -3
x+3 = 0
x+3 = 0
x+3 = 0 // - 3
x = -3
x in (-oo:-3) U (-3:+oo)
4/(5*x+15)-(1/(x+3)) = 3/5 // - 3/5
4/(5*x+15)-(1/(x+3))-(3/5) = 0
4/(5*x+15)-(x+3)^-1-3/5 = 0
4/(5*x+15)-1/(x+3)-3/5 = 0
(4*5*(x+3))/(5*(5*x+15)*(x+3))+(-1*5*(5*x+15))/(5*(5*x+15)*(x+3))+(-3*(5*x+15)*(x+3))/(5*(5*x+15)*(x+3)) = 0
4*5*(x+3)-1*5*(5*x+15)-3*(5*x+15)*(x+3) = 0
-15*x^2-5*x-90*x-135-15 = 0
-15*x^2-95*x-150 = 0
-15*x^2-95*x-150 = 0
-5*(3*x^2+19*x+30) = 0
3*x^2+19*x+30 = 0
DELTA = 19^2-(3*4*30)
DELTA = 1
DELTA > 0
x = (1^(1/2)-19)/(2*3) or x = (-1^(1/2)-19)/(2*3)
x = -3 or x = -10/3
-5*(x+10/3)*(x+3) = 0
(-5*(x+10/3)*(x+3))/(5*(5*x+15)*(x+3)) = 0
(-5*(x+10/3)*(x+3))/(5*(5*x+15)*(x+3)) = 0 // * 5*(5*x+15)*(x+3)
-5*(x+10/3)*(x+3) = 0
( x+10/3 )
x+10/3 = 0 // - 10/3
x = -10/3
( x+3 )
x+3 = 0 // - 3
x = -3
x in { -3}
x = -10/3
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