用科学记算器求得271,315,263,289,300,277,286,293,297,280的平均数为____ ,标准差为____ .(精确到0.1)
She's my mother. She's thin.
把多项式3x2y-5xy3+y2-2x3按x的降幂排列是____.
如图,点I和O分别是△ABC的内心和外心,则∠AIB和∠AOB的关系为( )