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2/3 = x^21 // - x^21
2/3-x^21 = 0
-1*x^21 = -2/3 // : -1
x^21 = 2/3
x^21 = 2/3 // ^ 1/21
x = (2/3)^(1/21)
x = (2/3)^(1/21)
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