Answer
$(r,-\theta)$
Work Step by Step
The polar graphs in this section exhibit symmetry. Visualize an xy-plane superimposed on the polar coordinate system, with the pole at the origin and the polar axis on the positive x-axis. Then a polar graph may be symmetric with respect to the x-axis (the polar axis), the y-axis( the line $\theta=\frac{\pi}{2}$) , or the origin (the pole).
Since, the missing ordered pair is reflection to angle $\theta$ which is $-\theta$.
Hence the desired result will be $(r,-\theta)$.
