7^765 * 7^450 * 7^-822 * 7^-389.
$$7^{765} * 7^{450} * 7^{-822} * 7^{-389}\\\
=7^{765+450-822-389}\\\\$$
$${\mathtt{765}}{\mathtt{\,\small\textbf+\,}}{\mathtt{450}}{\mathtt{\,-\,}}{\mathtt{822}}{\mathtt{\,-\,}}{\mathtt{389}} = {\mathtt{4}}$$
$$7^4 = 49^2=(50-1)^2=2500-100+1=2401$$
I've done a little more working than necessary because I didn't feel like using a calculator except I was lazy with the addition.