+115 Let \(r\) be the positive real solution to \(x^3 + \frac{2}{5} x - 1 = 0.\) Find the exact numerical value of \(r^2 + 2r^5 + 3r^8 + 4r^{11} + \dotsb.\)
+321 Why do you need help ASAP? Is this a homework question, or a test question, or something serious? If so, then we shouldn't answer it.
