its rst ue as hat the irst where A is a constant. b. If g(t) is not everywhere zero, assume that the solution of equation (48) is of the form y = (1) exp(- [p(1) dt). A'(t) where A is now a function of t. By substituting for y in the given differential equation, show that A(1) must satisfy the condition = g(1) exp(√p(1) dt). (50) (51) c. Find A(1) from equation (51). Then substitute for A(t) in equation (50) and determine y. Verify that the solution obtained in this manner agrees with that of equation (33) in the text. This technique is known as the method of variation of parameters; it is discussed in detail in Section 3.6 in connection with second- order linear equations. y' + t y' + y = cos(21), 1>0 old In each of Problems 29 and 30, use the method of Problem 28 to solve the given differential equation. 29. y' - 2y = 1²e²t 30.