According to Kepler's Third Law of Planetary Motion, the square of the time period of revolution ($T$) of a planet around the Sun is directly proportional to the cube of the semi-major axis ($R$) of its orbit.
The relationship is expressed as: $$T^2 \propto R^3$$
To find the proportionality for the time period ($T$), we take the square root of both sides: $$T \propto (R^3)^{1/2}$$ $$T \propto R^{3/2}$$
Final Answer: R^{3/2}
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