[填空题]
A spaceship in distress sends ou))jdw h-a 8fsuz,v xk(t two escape pods in opposite dbvg2v4 yt5a- yem/g,eirections. One travels at ,megye2g/t av4y-5b v a speed $v_1 =-0.60c$ in one direction, and the other travels at a speed $v_2 =+0.70c$ in the other direction, as observed from the spaceship. What speed does the first escape pod measure for the second escape pod? u = c
