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D( a )
a+3 = 0
5*a+15 = 0
a+3 = 0
a+3 = 0
a+3 = 0 // - 3
a = -3
5*a+15 = 0
5*a+15 = 0
5*a+15 = 0 // - 15
5*a = -15 // : 5
a = -15/5
a = -3
a in (-oo:-3) U (-3:+oo)
(8*a)/(5*a+15)-((a-8)/(a+3)) = 0
(8*a)/(5*a+15)+(-1*(a-8))/(a+3) = 0
(8*a*(a+3))/((5*a+15)*(a+3))+(-1*(a-8)*(5*a+15))/((5*a+15)*(a+3)) = 0
8*a*(a+3)-1*(a-8)*(5*a+15) = 0
3*a^2+49*a+120 = 0
3*a^2+49*a+120 = 0
3*a^2+49*a+120 = 0
DELTA = 49^2-(3*4*120)
DELTA = 961
DELTA > 0
a = (961^(1/2)-49)/(2*3) or a = (-961^(1/2)-49)/(2*3)
a = -3 or a = -40/3
(a+40/3)*(a+3) = 0
((a+40/3)*(a+3))/((5*a+15)*(a+3)) = 0
((a+40/3)*(a+3))/((5*a+15)*(a+3)) = 0 // * (5*a+15)*(a+3)
(a+40/3)*(a+3) = 0
( a+3 )
a+3 = 0 // - 3
a = -3
( a+40/3 )
a+40/3 = 0 // - 40/3
a = -40/3
a in { -3}
a = -40/3
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