In this paper, we establish some new modular equations of degree 9. We also establish several new $P$--$Q$ mixed modular equations involving theta–functions which are similar to those recorded by Ramanujan in his notebooks. As an application, we establish some new general formulas for explicit evaluations of a remarkable product of theta--functions.
"On some new modular relations for a remarkable product of theta--functions." Tbilisi Math. J. 7 (1) 55 - 68, 2014. https://doi.org/10.2478/tmj-2014-0006