....cos515=cos155,cos530=cos170,余弦在0~180是递减的，所以155<170,所以cos515=cos155>cos530=cos170sin(-54π/7)=sin(2π/7),sin(-63π/8)=sin(1π/8),正弦在0~90上为递增，所以sin(-54π/7)=sin(2π/7)>sin(-63π/8)=sin(1π/8),
