Write the volumes of the solids of revolution shown in Exercises 17-20 in terms of definite integrals that represent accumulations of shells. Do not solve the integrals. 17. y 2+ y = f(x) 18. 2 -1+ -2+ 19. y = f(x) 20. Y 2 3+ -3 1 y= f(x) y = f(x) -1 1