1-t2/t1 1-t2/t1, 1-t2/1+t2 1-t2/t1. There are any references about 1-t2/t1 in here. you can look below. 1-t2/t11-t2/t1 1-t2/1+t21-t2/1+t21-t2/t1, 1-t2/1+t2