Question 90683
This relation is not a function.

Proof:

x^2 = 1 + y^2

x = sqrt(1 + y^2)


Substitute y for 1:

x = sqrt(1 + 1^2)

  = sqrt(2)


Substitute y for -1:

x = sqrt(1 + (-1)^2)

  = sqrt(2)


Therefore, sqrt(2) has two y values: (√2, 1) and (√2, -1)