Phillip R. answered • 09/06/14
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You can use newton's method of approximation. Start with x = 1
f(x) = x3 + 4x - 8
f'(x) = 3x2 + 4
x1 = x - f(x) / f'(x) = 1 - (-3/7) = 10/7 = 1.42857
x2 = x1 - f(x1) / f'(x1) = 10/7 - (.629737/10.12245) = 1.3663
x3 = x2 - f(x2) / f'(x2) = 1.3663 - (.01635/4.02234) = 1.3648
The two other roots are imaginary
Saurav B.
09/06/14