L是區(qū)域D:x2+y2≤-2x的正向周界,則(x3-y)dx+(x-y2)dy等于:()
A.2π B.0 C.(3/2)π D.-2π
設(shè)L是從點(diǎn)(0,0)沿y=1-|x-1|至點(diǎn)(2,0)的折線段,則曲線積分-ydx+rdy等于()
A.0 B.-1 C.2 D.-2
設(shè)L是以A(-1,0)、B(-3,2)、C(3,0)為頂點(diǎn)的三角形邊界,沿ABCA方向,則曲線積分(3x-y)dx+(x-2y)dy等于()
A.-8 B.8 C.0 D.20