# A Challenging Problem of Solid Angle by HCR

Geometry Level 5

The diagram above shows a hollow circular section having its center O, inner radius $$r=6 \text{ cm}$$, outer radius $$R=20 \text{ cm}$$ & four identical rectangular slots each having width $$5 \text{ cm}$$ & length (depth) $$15 \text{ cm}$$ measured from the center $$O$$. Find out the solid angle (in Ste-radian) subtended by slotted section at the point $$P$$ lying at a distance $$OP = 5 \text{cm}$$ on the normal axis through the center $$O$$ (i.e. point $$P$$ lies normally outwards to the plane of paper.

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