9.4.48 Curvilinear integrals

Condition: Calculate the curved integral by a curve set parametrically: \ [\ begin {array} {l} \ int_ {l} y d x+x d y = i, \ quad \ text {where} l: x = r \ cos t \\ y = r \ sin t, \ quad 0 \ leq t \ leq \ frac {\ pi} {2} \ end {Array} \]