郭敦顒回答：r=a(sin(θ/3))^3 的全长,这题应是求定积分,积分区间为[0,6π],即积分下限为0,上限为6π,于是,r=∫a(sin(θ/3))^3 dθ,积分下限为0,上限为6π,换元,令α=θ/3,则dθ=3dα,sin(θ/3)= sinα,α的积分区间...