14. Find the solution of the initial value problem y′′ + y = F(t), y(0) = 0, y′(0) = 0, where F(t) = ⎧⎪⎨⎪⎩ At, 0≤ t ≤ ????, A(2???? − t), ???? < t ≤ 2????, 0, 2???? < t. Hint: Treat each time interval separately, and match the solutions in the different intervals by requiring that y and y′ be continuous functions of t.