An appropriate substitution for a. b. c. d. e. f. g. 2 x = 2 tan(20) for 0 e x = 20 for 0 e [ 2' u = In(x) = 0 for 0 e [n, 21t] x x = sec(20) for 0 e ( x 2' 5 x dx is f) 2' f)