noun
multivariate equation; equation with multiple unknowns
Mathematical term for an equation containing more than one variable. The glosses 'hypercomplex equation' and 'plural equation' are less common translations; 'multivariate equation' or 'simultaneous equations' are more standard in modern usage.
この多元方程式を解くには、少なくとも二つの式が必要だ。
To solve this multivariate equation, you need at least two equations.
連立方程式 refers specifically to a system of simultaneous equations, while 多元方程式 emphasizes the presence of multiple variables, which may or may not be part of a system.
Compound of 多元 (たげん, 'multivariate, pluralistic') and 方程式 (ほうていしき, 'equation'). The term is a straightforward technical coinage in mathematics.