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For the function below, approximate the area under the curve on the specified interval as directed. f ( x ) = = 12x "2 + 4x2 on [1, 3] with 4 subintervals of equal width and left endpoints for sample points X For each of the four subintervals of equal width Ax, consider the rectangle that has the subinterval as its base and height found by evaluating the function at the left endpoint of the subinterval. What is the numerical value of Ax? What are the left endpoints of each of the four subintervals? The approximate area under the curve is the sum of the areas of the four rectangles. Additional Materials Tutorial