LaTeXiT

Basic formula with eqnarray

just use the default setting 'Eqnarray' and typ the formula, without \begin{eqnarray} etc.

C_P(t) &=& \frac{F}{V_P} Dose K_a \biggl[ \frac{k_2 - \alpha}{(K_a - \alpha)(\beta-\alpha)} e^{-\alpha t} \biggr] \\

&&+ \frac{k_2-\beta}{(K_a-\beta)(\alpha-\beta)}e^{-\beta t} +\frac{k_2-K_a}{(K_a-\alpha)(K_a-\beta)}e^{-K_a t}