Polar Coordinates — Question 9

PDF ↗

Question 9

Problem

Find the smallest positive angle between the rays representing (3,17π/12)(3,17\pi/12) and (2,−π/4)(2,-\pi/4).

See the diagram in the original worksheet below.

Original worksheet page 1: question and worked solution for 3-6-009
Show solutionHide solution

Question 9 – Solution

See the diagram in the original worksheet below.

Solution

  1. Use the polar–Cartesian relationships x=rcos⁡θ,y=rsin⁡θ,r2=x2+y2.x=r\cos\theta,\qquad y=r\sin\theta,\qquad r^2=x^2+y^2. Equivalent polar coordinates satisfy (r,θ)=(r,θ+2kπ)=(−r,θ+(2k+1)π).(r,\theta)=(r,\theta+2k\pi)=(-r,\theta+(2k+1)\pi).

  2. Apply the identity that matches the requested conversion, symmetry test, or intersection, and then check the resulting point or curve in the original polar equation.

  3. Reduce angles to 17π/1217\pi/12 and 21π/1221\pi/12.

  4. Their smaller difference is π/3\boxed{\pi/3}.

Original worksheet page 2: question and worked solution for 3-6-009

Original worksheet layout. Use Enlarge or open the PDF for a closer view.