1. On his 25th birthday, the astronaut twin leaves on a long space journey at an average speed of v/c= 0.98. He returns after 20 earth-years have elapsed, to celebrate his earth-twin's 45th birthday. Compare their biological ages. 2. 1/ square root 1- v^2/c^2, My teacher is using v/c instead of giving me a velocity which is throwing me off, I'm not sure if I square the .98 or not. 3. 1/ square root 1- v^2/c^2, so what I was doing was putting the .98 and squaring it, which gives me .9604. I subtracted the 1 from .9604, and got .0396. I inverse the .0396 and get an answer of 25.25...Do I add that 25.25 to the original age of the astronaut which would give me an answer of 50.25 or is the astronauts age just 25.25...?