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D( x )
3*x+15 = 0
4*x+20 = 0
3*x+15 = 0
3*x+15 = 0
3*x+15 = 0 // - 15
3*x = -15 // : 3
x = -15/3
x = -5
4*x+20 = 0
4*x+20 = 0
4*x+20 = 0 // - 20
4*x = -20 // : 4
x = -20/4
x = -5
x in (-oo:-5) U (-5:+oo)
2/(4*x+20)-(8/(3*x+15)) = 0
2/(4*x+20)-8*(3*x+15)^-1 = 0
2/(4*x+20)-8/(3*x+15) = 0
(2*(3*x+15))/((4*x+20)*(3*x+15))+(-8*(4*x+20))/((4*x+20)*(3*x+15)) = 0
2*(3*x+15)-8*(4*x+20) = 0
-26*x-130 = 0
(-26*x-130)/((4*x+20)*(3*x+15)) = 0
(-26*x-130)/((4*x+20)*(3*x+15)) = 0 // * (4*x+20)*(3*x+15)
-26*x-130 = 0
-26*x-130 = 0 // + 130
-26*x = 130 // : -26
x = 130/(-26)
x = -5
x in { -5}
x belongs to the empty set
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