Calculate the synodic period of a planet if its period of revolution around the Sun is 4.5 years.

According to the condition of the problem, the period of revolution of the planet around the Sun is 4.5 years, therefore, this is the outer planet. Therefore, to calculate the synodic period, we will use the formula 1 / S = 1 / P-1 / T -, where P = 1 year is the period of the Earth’s revolution around the Sun, T is the period of the planet’s revolution around the Sun. 1 / S = 1 – 1 / 4.5 = 0.88888; S = 1.125 (years).