11. Let g(x) = f(2x). Show that the average value of f on the interval [0, 26] is the same as the average value of g on the interval [0, 6]. 12. (8x + 12)2 der 13. 2 sin" (x) cos(x) dr 14. EV12 - 3 dx 15. 5it* sin (15) dt : 16. (21 + 7) 17. Ar + 5 da 18. sin (2t) dt 1.5 19. 10(2x - 3)1 de 20. r vx - 10 der 21. x(x - 7)12 de