Identify which of the following is a Fermat-Pell equation.
x2−Dy2=1x^2 - Dy^2 = 1x2−Dy2=1
ax+by=cax + by = cax+by=c
x2+y2=z2x^2 + y^2 = z^2x2+y2=z2
x3+y3=z3x^3 + y^3 = z^3x3+y3=z3