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D( x )
15*x+45 = 0
15*x+45 = 0
15*x+45 = 0
15*x+45 = 0 // - 45
15*x = -45 // : 15
x = -45/15
x = -3
x in (-oo:-3) U (-3:+oo)
(6*x+48)/(15*x+45) = 0
6*x+48 = 0 // - 48
6*x = -48 // : 6
x = -48/6
x = -8
x = -8
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