√2x-1=t x=5时,t=3 ; x=1时,t=1
t^2=2x-1
x=(t^2+1)/2
dx=dt
代入原式：
＝f (1, 3) (t^2+1)/(2t)dt
=f(1,3) (1/2t+1/(2t))dt
=1/4t^2+1/2lnt (1,3)
=(9/4+1/2ln3)-1/4
=2+1/2ln3
再问： 不对啊 答案是16/3
再答： √2x-1=t x=5时，t=3 ; x=1时，t=1
t^2=2x-1
x=(t^2+1)/2
dx=tdt （这里做错了）
代入原式：
＝f (1, 3) [(t^2+1)/(2t)]tdt
=1/2f(1,3) (t^2+1)dt
=1/2 (1/3t^3+t)(1,3)
=1/2 (9+3-1/3-1)
=1/2(12-4/3)
=6-2/3
=16/3
