∫（1/3)^√xdx
=∫2√x(1/3)^√xd√x
=2∫√x(1/ln(1/3))d(1/3)^√x
=[2/ln(1/3)]∫√xd(1/3)^(√x)
=(-2/ln3)√x*(1/3)^√x +(2/ln3)∫(1/3)^√xd√x
=(-2/ln3)√x*(1/3)^√x-2/(ln3)^2 *(1/3)^√x +C能用簡單點的方法直接判斷他收斂嗎？an=(1/3)^(√n)an+1=(1/3)^√(n+1)an+1/an=(1/3)^(√n+1-√n)<1