4. (a) Let D be the region located in the first quadrant of R? between the two circles of radii 1 and 4 centered on the origin. Evaluate sin(a2 + y?))x dædy . (b) Consider the thin disk centered on...

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Extracted text: 4. (a) Let D be the region located in the first quadrant of R? between the two circles of radii 1 and 4 centered on the origin. Evaluate sin(a2 + y?))x dædy . (b) Consider the thin disk centered on the origin in R? of radius 1. Suppose it is made of a material with mass density function x?y? 1+ x2y2 p(x, y) — еxp in grams per units of area. Show that the mass of the disk does not exceed re grams.