
Special Relativity #3
The captain of a the spaceship Red Dwarf is travelling directly towards Earth at a speed of 0.72c relative to the planet. At the same time the spaceship Soylent Green is flying directly away from Earth, directly towards the Red Dwarf, with a speed of 0.87c relative to the planet. According to the captain of the Red Dwarf, how fast is the Soylent Green travelling? Give your answer as a multiple of 'c', the speed of light in vacuum.
what I did is
ux`=uxv/(1vux/c^2)
and there fore
= 0.72c0.87c / (1(0.87*0.72)/3.0e^8^2))
and got 1.5c
which is not right