中点法と台形法

The trapezoidal rule divides the total interval into equal subintervals and connects the endpoints of each subinterval with a straight line, forming trapezoids. The area of each trapezoid is calculated as the average of its two vertical sides multiplied by the horizontal width. Summing all trapezoid areas yields an approximation of the total area under the curve, making it a key method in approximate integration.

Interior velocities appear twice because each interior point belongs to two adjacent trapezoids. The first and last velocities appear only once, at the boundaries of the total interval. This pattern emerges when combining like terms after summing all individual trapezoid areas.

The trapezoidal rule estimates displacement when velocity data is available at discrete time intervals rather than as a continuous function. By approximating the area under a velocity-time graph, it calculates the total distance traveled by a vehicle or object over a specified time period, making it valuable for analyzing empirical motion data.

Increasing the number of equal subintervals improves the accuracy of the trapezoidal rule approximation. With more subintervals, the straight lines connecting endpoints more closely follow the actual curve, resulting in a more reliable estimate of the total area or displacement, especially for time-dependent processes.

In a velocity-time graph, each trapezoid has two vertical sides representing the velocities at the beginning and end of a time segment, and a horizontal base representing the time interval width. The area of this trapezoid represents the approximate displacement during that specific time segment.

The trapezoidal rule is a fundamental technique in numerical analysis preferred when empirical data is available at discrete points and a continuous function is unavailable. It provides a practical, straightforward approach to integrating motion or other time-dependent processes without requiring complex calculations or assumptions about underlying function behavior.