Identity (Equation or Inequality)
An equation which is true regardless of what
values are substituted for any variables (if there are any variables
at all).
Identities: 
1 + 1 = 2
(x + y)^{2} = x^{2} + 2xy + y^{2}
a^{2} ≥ 0
sin^{2} θ + cos^{2} θ = 1 
See
also
Conditional
equation, conditional
inequality, trig
identities
