∫dx/(4-x^2)
let
x= 2siny
dx = 2cosydy
∫dx/(4-x^2)
=(1/2) ∫secy dy
= (1/2)ln|secy+tany|+ C
=(1/2)ln|2/√(4-x^2) + x/√(4-x^2) | + C麻烦求下（4-x²）负二次方的积分？