### orthogonal curves

Two (or more) intersecting curves that are vertical at their intersection are above-mentioned to be orthogonal.

### How do you know if two curves are orthogonal?

Two curves are above-mentioned to be orthogonal if their tangent lines are vertical at [see ail] fix of intersection. Two families of curves are above-mentioned to be orthogonal if [see ail] incurve in one family is orthogonal to [see ail] incurve in the fuse family.