1/（2 - cos^2 t）=1/(√2-cost)(√2+cost)=(1/(2√2) *2√2)/(√2-cost)(√2+cost)
=1/(2√2) *((√2-cost)+(√2+cost))/(√2-cost)(√2+cost)
=1/2√2 * [ 1/（√2-cost)+1/(√2+cost) ]
所以有：
- ∫dcost）/（2 - cos^2 t）
= - 1/2√2 * ∫[ 1/（√2-cost)+1/(√2+cost) ]d(cost)