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x in (-oo:+oo)
(2/5)^6-x = 5/2 // - 5/2
(2/5)^6-x-(5/2) = 0
(2/5)^6-x-5/2 = 0
-x-77997/31250 = 0 // + 77997/31250
-x = 77997/31250 // * -1
x = -77997/31250
x = -77997/31250
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