[填空题]
A spaceship leaves Earth rlof smi-gsx,;(c pty219 c 4gtraveling at 0.71c. A second spac9 odv-(8cfg 4t(rgr )5j85+imqmwvoiho(b hueship leaves the first at a speed of 0.87c with respect to the first. Calculate the speed of the second ship with respect to Earth if it ish h)5 u g4iim8r g-oo(b+(8fqdrj5v c(o9mtvw fired
(a) in the same direction the first spaceship is already moving, u = c
(b) directly backward toward Earth.u = c
