8.** Let R be the region bounded by the square with vertices (0, 1), (1, 2), (2, 1), (1, 0). Evaluate the integral ((x + y)²sin²(x - y)) dA. (15 分)
7. Find the curvature of the parabola given by y = x -x² at x = 2, and sketch the circle of curvature at (2, 1). (15 分)
6. Evaluate dx. (15 分)