Use the method of Frobenius to find the first four nonzero terms in the series expansion about x= 0 for a solution to the given linear third-order equation for x> 0. 7xy" + 15x?y" - 6xy' - (x- 6)y = 0 What are the first four terms for the series? y(x) = (Type an expression in terms of a, that includes all terms up to order 4.) +..