4. Find a general solution to y" - 2y' + y = e^t/t^2+1 by variation of parameter method.
5. Solve the non-homogeneous differential equation: y" - 2y' + 2y = et sec (t).
6. Solve the following PDE
a) pq + p + q = 0
b) z = px + qy+p² + pq+q²
c) q = px + p²
d) q² = yp³ 7.
7. Find the Laplace transform of the following
a) (t² + 1)² + 3 cosh (5t) - 4 sinh(t)
b) e-5t (t4 + 2t² + t)