linear constraint

例句：

1. 1. The line of the road is straight as an arrow.
   这条路线直得像箭一样。
2. 2.The linear equation represents a straight line in a coordinate plane.
   这个线性方程在坐标平面上表示一条直线。
3. 3.The linear programming problem requires finding the maximum value of a function subject to certain constraints.
   线性规划问题需要找到函数的最大值，同时满足某些约束条件。