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((x² + y²)³ )æ dxdy . D (b) Consider the thin disk centered...

Need help with part (b). Thank you :)

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((x² + y²)³ )æ dxdy . D (b) Consider the thin disk centered on the origin in R² of radius 1. Suppose it is made of a material with mass density function P(x, y) = exp 1+ a²y² in grams per units of area. Show that the mass of the disk does not exceed ne grams.