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Let r be the positive real solution to x^3 + 2/5 x - 1 = 0. Find the exact numerical value of r^2 + 2r^5 + 3r^8 + 4r^11 + ....

 Feb 15, 2020
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r = ~0.86756

 

 ∑[ n*0.86756^(3n -1), n, 1, ∞] = ~6.25 

 Feb 15, 2020

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