The trapezoidal method splits the area under a curve into trapezoids, calculates the area of each trapezoid, and sums the individual areas to approximate the total area under the curve, which represents the definite integral. It uses the formula: Integral = (h/2) * (y0 + 2*y1 + 2*y2 + ... + 2*yn-1 + yn), where h is the width of each interval between the x-values x0, x1, etc., and y0, y1, etc. are the corresponding y-values of the function. Simpson's 1/3 Rule similarly divides the interval into sub-intervals, but approximates each using a quadratic curve