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Tuesday, November 29, 2016

2016/109) Let -1 <=p <=1. Show that the equation 4x^3-3x-p=0 has a unique root in the interval [\frac{1}{2}, 1] find it.

because p is between -1 and 1 so cos^{-1}p is defined. let x = \cos\,t so we get
\cos\, 3t = p
and hence 3t = \arccos p and so x = \frac{1}{3}\cos^{-}p
if x > 1 we get 4x^3-3x > 1 and if x < \frac{1}{2} we get 4x^3 - 3x < -1 and out side the
limit so x is between \frac{1}{2} and 1

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