俄罗斯的地形以叶尼塞河为界,西部主要是____,东部多____。
— Han Tao _______ for school at seven o'clock in the morning.
— That's too early.
定义运算“△”:对于任意实数a,b且a≥b时,都有a△b=a2﹣ab+b2,如5△4=52﹣5×4+42=21,若(x﹣3)△4=21,则实数x的值为____.
读“我国南部沿海区域”图,完成以下问题.