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Evaluate m1arctan(1m)=\sum_{m \geq 1}\arctan\left(\frac{1}{\sqrt{m}}\right)=

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Q. Evaluate m1arctan(1m)=\sum_{m \geq 1}\arctan\left(\frac{1}{\sqrt{m}}\right)=
  1. Recognize Infinite Series: To evaluate the infinite sum of arctan(1m)\arctan(\frac{1}{\sqrt{m}}) for mm starting from 11, we need to recognize that this is an infinite series and there is no straightforward formula to directly calculate the sum of an arctan\arctan series. However, we can check if the series converges and then possibly use numerical methods or known convergent series to estimate the sum.
  2. Check Convergence: First, we need to check if the series converges. We can use the comparison test by comparing our series to a known convergent series. The series (1/m)\sum(1/\sqrt{m}) is a p-series with p=1/2p = 1/2, which is known to diverge because p1p \leq 1. However, since arctan(x)x\arctan(x) \leq x for all xx in [0,1][0,1], the series arctan(1/m)\sum\arctan(1/\sqrt{m}) will converge if (1/m)\sum(1/\sqrt{m}) converges. Since we know (1/m)\sum(1/\sqrt{m}) diverges, we cannot conclude convergence from this comparison.
  3. Use Comparison Test: Another way to check for convergence is to use the integral test. The function f(m)=arctan(1m)f(m) = \arctan(\frac{1}{\sqrt{m}}) is continuous, positive, and decreasing for m1m \geq 1. We can set up the integral from 11 to infinity of arctan(1x)dx\arctan(\frac{1}{\sqrt{x}}) \, dx to check for convergence.
  4. Calculate Integral: We calculate the integral arctan(1/x)dx\int \arctan(1/\sqrt{x}) \, dx from 11 to infinity. To integrate arctan(1/x)\arctan(1/\sqrt{x}), we can use a substitution. Let u=1/xu = 1/\sqrt{x}, which means x=1/u2x = 1/u^2 and dx=2/u3dudx = -2/u^3 \, du. The limits of integration change accordingly: when x=1x = 1, u=1u = 1, and when xx approaches infinity, uu approaches 1100.
  5. Substitution Error: Substituting into the integral, we get arctan(u)(2u3)du\int \arctan(u) \cdot \left(-\frac{2}{u^3}\right) du from u=1u = 1 to u=0u = 0. This integral is not straightforward to evaluate, and it seems we have made a mistake in the substitution step. The correct substitution should be u=1xu = \frac{1}{\sqrt{x}}, which means dx=2u3dudx = -2u^3 du, not 2u3du-\frac{2}{u^3} du. This is a math error.

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