r+s-t-(r-s+t)
=2s-t is the answer
People think this answer would be just =2s but I have verified with an online calculator and the answer that textbooks look for regarding this is 2s-t
You would assume you would go r-r and thats 0 so no r's
you would say s-(-s) makes it plus and theres 2s
and you would say -t -(+t) is -t
that's why the answer is 2s-t
At first I also did t-(+t) and thought it would be no t's but the answer is in fact 2s-t