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Find the length of the spiral 
r=theta for 
0 <= theta <= 2.

Find the length of the spiral r=θ r=\theta for 0θ2 0 \leq \theta \leq 2 .

Full solution

Q. Find the length of the spiral r=θ r=\theta for 0θ2 0 \leq \theta \leq 2 .
  1. Calculate spiral length: Calculate the length of the spiral using the integral formula for polar coordinates: L=r2+(drdθ)2dθL = \int \sqrt{r^2 + \left(\frac{dr}{d\theta}\right)^2} d\theta.
  2. Find drdθ:\frac{dr}{d\theta}: First, find drdθ\frac{dr}{d\theta}. Since r=θr=\theta, drdθ=dθdθ=1\frac{dr}{d\theta} = \frac{d\theta}{d\theta} = 1.
  3. Plug into integral formula: Now, plug r=θr=\theta and drdθ=1\frac{dr}{d\theta}=1 into the integral formula: L=02θ2+12dθL = \int_{0}^{2} \sqrt{\theta^2 + 1^2} d\theta.
  4. Simplify integral: Simplify the integral: L=02θ2+1dθL = \int_{0}^{2} \sqrt{\theta^2 + 1} \, d\theta.
  5. Use trigonometric substitution: Now we need to solve the integral. This is a bit tricky, but we can use a trigonometric substitution or look up the integral in a table.
  6. Change limits of integral: Let's use a trigonometric substitution. Set θ=tan(u)\theta = \tan(u), then dθ=sec2(u)dud\theta = \sec^2(u) \, du.
  7. Simplify integral with identity: When θ=0\theta=0, u=0u=0, and when θ=2\theta=2, u=arctan(2)u=\arctan(2). So we need to change the limits of the integral.
  8. Complex integral solution: The integral becomes L=0arctan(2)tan2(u)+1sec2(u)duL = \int_{0}^{\arctan(2)} \sqrt{\tan^2(u) + 1} \sec^2(u) \, du.
  9. Final integral result: Simplify the integral using the identity tan2(u)+1=sec2(u)\tan^2(u) + 1 = \sec^2(u): L=0arctan(2)sec3(u)duL = \int_{0}^{\arctan(2)} \sec^3(u) \, du.
  10. Final integral result: Simplify the integral using the identity tan2(u)+1=sec2(u)\tan^2(u) + 1 = \sec^2(u): L=0arctan(2)sec3(u)duL = \int_{0}^{\arctan(2)} \sec^3(u) \, du.This integral is still complex, but we can look it up or use a reduction formula. The result is L=[12sec(u)tan(u)+12lnsec(u)+tan(u)]0arctan(2)L = \left[\frac{1}{2} \sec(u) \tan(u) + \frac{1}{2} \ln|\sec(u) + \tan(u)|\right]_{0}^{\arctan(2)}.

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