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The side of the spherical triangle between the z-axis and the x-axis labeled, elevation plane. The side of the spherical triangle between the z-axis and the x-axis labeled, azimuth plane. A square pyramid R is inscribed inside the spherical triangle. The apex of the pyramid lies in the origin of the system. The base length of the pyramid along the azimuth plane labeled, R sine of theta d phi. The region on the azimuth plane along the base side of the pyramid labeled, R d phi. The region on the elevation plane along the base side of the pyramid labeled, R d theta. The base region of the pyramid labeled, d A equals R squared sine of theta d theta d phi equals R squared d ohm. The x-axis makes an angle phi with the region on the azimuth plane. The z-axis makes an angle theta with the region on the elevation plane.