noun
system of equations
Mathematical term referring to a set of equations to be solved simultaneously.
この方程式系を解くには、行列を使うと便利です。
To solve this system of equations, it is convenient to use matrices.
連立方程式 specifically refers to simultaneous equations, while 方程式系 is a broader term for any system of equations.
Compound of 方程式 (equation) and 系 (system).