完整清楚过程rt所示…希望能帮到你解决问题
思路：换成极坐标。x = rcosu, y = rsinu原积分 = ∫[0, pi/4] du ∫ [0, sinu/cos^2 u] 1/r r dr = ∫[0, pi/4] sinu/cos^2 udu = secu from 0 to pi/4 = sqrt(2) - 1
