What is the plane of the calculus medium and French?

French plane is a mathematical term, which refers to the cut point of the passing curve and perpendicular to the cut line, which is called the French plane. That is, the plane of the cut line.
The cut point of the space curve, and vertical planes with the cut line, called the French plane. That is, the plane vertical on the virtual method line. For example, the center of the sphere is the endpoint of the endpoint, and the cut surface where the sphere is located is the plane (method surface).
Themology includes the operation of the number of guidance, so that the slope of functions, speed, acceleration and curves can be discussed with a set of common symbols. Integration, including the calculation of points, provides a set of common methods for defining and calculating area and volume.
Folding geometric meaning
Set Δx is an increase on the horizontal coordinates of the point m on the curve y = f (x). DY is the incremental increase of the curve at the cut line of the point m. When | Δx | is very hour, | Δy -dy | Δx | is much smaller (high -level infinite), so at the point M, we can use the cut segment to approximate the curve segment.
The above content reference: Baidu Encyclopedia-Calculus

French plane is a little on the relatively curve.
This point on the curve, and the plane of the cut line direction of the curve at the point at the point is the plane of the curve at the point. Figure above