19.) Consumer consumes only goods x and y. Find the marginal rate of substitution of the following utility function and graph the indifference curve.\
a.) $U(x,y) = \sqrt{xy}$\
b.) $f(x,y) = x + xy + y$\
c.) $U(x,y) = \sqrt{x^2 + y^2}$\
d.) $U(x,y) = x^\alpha y^\beta$\
e.) $U(x,y) = \frac{xy}{x+y}$
