(b) Determine whether the following DE 6xy dy + (4x + 9y?) dx = 0. is exact, if the DE is not exact then find an appropriate integrating factor for the DE to be exact, and hence find the general solution of the DE.2. (a) Prove that the substitution u = y\"" reduces the Bernoulli's equation ::+ P(x}y = f{x)y". n i U, n =95 1 to a linear equation in u. {b} Find the solution of the nonlinear I'u'P x 21y = 3:113. y(1) =