Step-by-step explanation:
1. Two points are generally interpreted as naming the shorter arc of a circle. If the longer arc is intended, it must be identified differently some way. It is easier to add a third point and say "arc ACB" than to say "long arc AB".
___
2. If you didn't already know that 135° = 3/4 of a half-circle, hence 3/4π radians, then you could figure it out from ...
135° = 135°×(π/180°) radians = π × (135/180)
Reducing the fraction 135/180 without a calculator can proceed several ways. One is ...
135/180 = 270/360 = 27/36 = (3·9)/(4·9) = 3/4
Now, you know that ...
135° = 3π/4 radians
__
In general, a calculator will give you a numerical answer, such as 2.3561945 radians. If you want a numerical answer and don't have a calculator, you can use the ratio 355/113 for π and then do the long division. Only 6 significant figures will be accurate using this ratio.
(3/4)·(355/113) = 1065/452 ≈ 2.35619 . . . . radians