※ 引述《graydevils (why, or why not)》之銘言：
: 4 √(x^2-4)
: ∫ ----------- dx
: 2 x
let x = 2sec@ , √(x^2-4) = 2tan@ , dx = 2sec@tan@d@
√(x^2-4) π/3 2tan@ π/3 2
∫ ----------- dx = ∫ -------2sec@tan@ d@ = 2 ∫ tan @ d@
x 0 2sec@ 0
π/3 2 π/3
= 2 ∫ (sec @ - 1 ) d@ = 2 ( tan@ - @ )| = 2√3 - 2π/3
0 0
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