Let u: R2 R be a strictly increasing C utility function. + (a) Derive an expression for the slope of an indifference curve at an arbitrary consumption bundle (xo, yo) R. '++ (b) Take a derivative of the expression in part (a) in order to compute the second-order derivative of the indifference curve. Demonstrate this second-order derivative is positive (i.e. the law of diminishing marginal rate of substitution holds) if u is quasiconcave on IR.