How does refractive index ($μ$) of a material vary with respect to wavelength (λ)? A and B are constants

$μ = A + Bλ^2$ $μ = A +\frac{B}{λ^2}$ $μ = A + Bλ$ $μ = A +\frac{B}{λ}$

$μ = A +\frac{B}{λ^2}$

Cauchy's formula is $μ = A +\frac{B}{λ^2}$