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D( x )
100-x = 0
100-x = 0
100-x = 0
100-x = 0 // - 100
-x = -100 // * -1
x = 100
x in (-oo:100) U (100:+oo)
31000 = (2750*x)/(100-x) // - (2750*x)/(100-x)
31000-((2750*x)/(100-x)) = 0
31000-2750*x*(100-x)^-1 = 0
(-2750*x)/(100-x)+31000 = 0
(-2750*x)/(100-x)+(31000*(100-x))/(100-x) = 0
31000*(100-x)-2750*x = 0
3100000-33750*x = 0
(3100000-33750*x)/(100-x) = 0
(3100000-33750*x)/(100-x) = 0 // * 100-x
3100000-33750*x = 0
3100000-33750*x = 0 // - 3100000
-33750*x = -3100000 // : -33750
x = -3100000/(-33750)
x = 2480/27
x = 2480/27
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