积分上限是π/2,积分下限是0?
∫dx/(12+13cosx),（π/2,0）
=(1/5)ln|[tan(x/2)+5]/[tan(x/2)-5]|,（π/2,0）
=(1/5)ln|[tan(π/4)+5]/[tan(π/4)-5]|-(1/5)ln|(tan0+5)/(tan0-5)|
=(1/5)ln|6/(-4)|-(1/5)|5/(-5)|
=(ln1.5)/5-(ln1)/5
=(ln1.5)/5
≈0.08109302