`a, x^3 + 15x^2 + 75x + 125 = 0`
`x^3 + 3 . x^2 . 5 + 3 . x . 5^2 + 5^3 = 0`
`(x + 5)^3 = 0`
`x + 5 = 0`
`x = -5`
`b, x^3 + 48x = 12x^2 + 64`
`x^3 - 12x^2 + 48x - 64 = 0`
`x^3 - 3 . x^2 . 4 + 3 . x . 4^2 - 4^3 = 0`
`(x - 4)^3 = 0`
`x - 4 = 0`
`x = 4`
`c, (5x - 1) - 196 = 0`
`5x - 1 = 196`
`5x = 197`
`x = 197/5`
`d, 1/(27x^3) - 1/(3x^2) + x = 1`
`1/(27x^3) - 1/(3x^2) + x - 1 = 0`
`[1/(3x)^3] - 3 . 1/(9x^2) . 1 + 3 . 1/(3x) . 1^2 - 1^3 = 0`
`[1/(3x) - 1]^3 = 0`
`1/(3x) - 1 = 0`
`1/(3x) = 1`
`3x = 1`
`x = 1/3`
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