[C] (mathematics 数) statement that two expressions (connected by the sign =) are equal, eg 2x + 5 = 11 等式（如2x + 5 = 11）. 
[U] action of making equal or regarding as equal 等同; 相等: The equation of wealth with happiness can be dangerous. 把财富与幸福等同起来有时候很危险.