A baseball is thrown straight downward with an initial speed of 40 ft/s from the top of the Washington Monument (555 ft high). How long does it take to reach the ground, and with what speed does the baseball strike the ground? 2. Verify the solution by substitution: y" + 4y = 0; y = cos(2x) 3. Substitute y = ex to determine all values of the constant r such that y = ex is a solution of 3y" + 3y - 4y = 0.