If you memorize the photosynthesis equation, you've also memorized the cellular respiration equation. That's because respiration is the exact opposite as photosynthesis with one small difference.
The most important chemical equation in the world is the following: carbon dioxide plus water plus energy from sun equals sugar plus oxygen (6 CO2) + (6 H20) + (674 calories) = (C6H1206) + (6 02).