Functions as special relations
Sets, relations and functions · Mathematics
Study notes
Q: Which are functions? (a) {(1,2),(2,3),(1,4)} (b) {(1,2),(2,3),(3,4)} (c) x^2 + y^2 = 1. (a) Not a function: input 1 has two outputs (2 and 4). (b) Function: each input one output. (c) Not a function: vertical line x = 0 hits circle twice.