23} Consider the function {[16,}? = II] + x3 3x Exy + 3;\". Suppose we want to use the numerical algorithm to nd a solution for any such that f {12, y) = 7:". Suppose we start with x = y = {18. Use the Taylor series to nd the heat changes of x and y {in the second step], so that we can converge to a solution most efciently, that is, we can reach {(1:3) = 'i" fast. 24} Use matrix algebra to prove that any random variable has a nonnegative variance