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D( x )
48-x = 0
48-x = 0
48-x = 0
48-x = 0 // - 48
-x = -48 // * -1
x = 48
x in (-oo:48) U (48:+oo)
2.5 = x/(48-x) // - x/(48-x)
2.5-(x/(48-x)) = 0
(-1*x)/(48-x)+2.5 = 0
(-1*x)/(48-x)+(2.5*(48-x))/(48-x) = 0
2.5*(48-x)-1*x = 0
120-3.5*x = 0
(120-3.5*x)/(48-x) = 0
(120-3.5*x)/(48-x) = 0 // * 48-x
120-3.5*x = 0
120-3.5*x = 0 // - 120
-3.5*x = -120 // : -3.5
x = -120/(-3.5)
x = 34.28571429
x = 34.28571429
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