11. Let x [n] be real WSS with correlation r [m] which is assumed known. The second order prediction is formulated as follows. Define e [n] via: e [n] = x [n] + ax [n 1] + ax [n- 2] We want to find the coefficients a, a2 such that e [n] 1 x [n 1] and e[n] x [n-2]. Formulate each condition as an appropriate expectation, and simplify to obtain two lin- ear equations in the two unknowns a, a2, where the coefficients in the linear equations are appropriate values of r [m].