Exercises 4.7 answers to odd-numbered problems begin on page a-9. in problems 1-24 solve each differential equation by variation of parameten state an interval on which the general solution is defined. 1. y" +y sec x 3. y" +y sin 5. y" +y cosx 7. y" - y cosh x 2. y" y tan x 4. y" +y secx tan x 6, y" + y = sec2x 8. y" -y sinh 2r 11. y" +3y' + 2y 1/e 12. y"-3y' 2y e+e) 13. y" 3y'+2y sin e 15. y"-2y' + y = ey(1 + x2) 16. y"-2y' + 2y = exsecx 17. y" + 2y, + y = e-rin x 14. y" -2y' +y-e' arctan x 18. y" + 10y' + 25y = e-i%2