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D( s )
s-13 = 0
s-13 = 0
s-13 = 0
s-13 = 0 // + 13
s = 13
s in (-oo:13) U (13:+oo)
3/(s-13) = s/10 // - s/10
3/(s-13)-(s/10) = 0
3/(s-13)-s/10 = 0
(3*10)/(10*(s-13))+(-s*(s-13))/(10*(s-13)) = 0
3*10-s*(s-13) = 0
13*s-s^2+30 = 0
13*s-s^2+30 = 0
13*s-s^2+30 = 0
DELTA = 13^2-(-1*4*30)
DELTA = 289
DELTA > 0
s = (289^(1/2)-13)/(-1*2) or s = (-289^(1/2)-13)/(-1*2)
s = -2 or s = 15
(s+2)*(s-15) = 0
((s+2)*(s-15))/(10*(s-13)) = 0
((s+2)*(s-15))/(10*(s-13)) = 0 // * 10*(s-13)
(s+2)*(s-15) = 0
( s+2 )
s+2 = 0 // - 2
s = -2
( s-15 )
s-15 = 0 // + 15
s = 15
s in { -2, 15 }
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