a) State the principle of comparison for integrals. b) Let f(x,y) = sqrt (3-x-y). Plot some level sets of f inside the unit disc x² + y² s 1, marking the level value for each. Include at least one which is reduced to a single point. c) Using the comparison principle, give an upper bound to //o f(x,y) dA, where D is the unit disc (see above). 1 X A- Ff T: BIUS x2 x²