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D( x )
x-15 = 0
x+15 = 0
x^2-225 = 0
x-15 = 0
x-15 = 0
x-15 = 0 // + 15
x = 15
x+15 = 0
x+15 = 0
x+15 = 0 // - 15
x = -15
x^2-225 = 0
x^2-225 = 0
1*x^2 = 225 // : 1
x^2 = 225
x^2 = 225 // ^ 1/2
abs(x) = 15
x = 15 or x = -15
x in (-oo:-15) U (-15:15) U (15:+oo)
2/(x+15)-(3/(x-15)) = (4*x)/(x^2-225) // - (4*x)/(x^2-225)
2/(x+15)-(3/(x-15))-((4*x)/(x^2-225)) = 0
2/(x+15)-3*(x-15)^-1-4*x*(x^2-225)^-1 = 0
2/(x+15)-3/(x-15)+(-4*x)/(x^2-225) = 0
(2*(x-15)*(x^2-225))/((x+15)*(x-15)*(x^2-225))+(-3*(x+15)*(x^2-225))/((x+15)*(x-15)*(x^2-225))+(-4*x*(x+15)*(x-15))/((x+15)*(x-15)*(x^2-225)) = 0
2*(x-15)*(x^2-225)-3*(x+15)*(x^2-225)-4*x*(x+15)*(x-15) = 0
225*x-x^3-4*x^3-75*x^2+900*x+16875 = 0
1125*x-5*x^3-75*x^2+16875 = 0
1125*x-5*x^3-75*x^2+16875 = 0
5*(225*x-x^3-15*x^2+3375) = 0
225*x-x^3-15*x^2+3375
15*(225-x^2)-x^3+225*x
x*(225-x^2)+15*(225-x^2)
(x+15)*(225-x^2)
5*(x+15)*(225-x^2) = 0
(5*(x+15)*(225-x^2))/((x+15)*(x-15)*(x^2-225)) = 0
(5*(x+15)*(225-x^2))/((x+15)*(x-15)*(x^2-225)) = 0 // * (x+15)*(x-15)*(x^2-225)
5*(x+15)*(225-x^2) = 0
( 225-x^2 )
-1*x^2 = -225 // : -1
x^2 = 225
x^2 = 225 // ^ 1/2
abs(x) = 15
x = 15 or x = -15
( x+15 )
x+15 = 0 // - 15
x = -15
x in { 15}
x in { -15}
x belongs to the empty set
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