LaTex, align alignment characters between align blocks
I would like to align two alignment characters between two align blocks so that I can have some text in the middle of a derivation with equations maintaining the horizontal alignment. For example the following excerpt of latex using align \begin{align*} \frac{\delta \phi}{\delta x_1} = {} &\frac{9}{8}\frac{\delta_1\phi}{\delta_1x_1...