电阻R1两端的电压是2V,求:
若a=1﹣2,先化简再求a2-1a2+a+a2-2a+1a2-a的值.
—What time do you usually go to bed? —I usually go to bed _________ eight o'clock.
下列条件:①三角形的一个外角与相邻内角相等;②∠A=12∠B=13∠C;③AC:BC:AB=1:3;2 ④AC=n2-1,BC=2n,AB=n2+1(n>1).能判定△ABC是直角三角形的条件个数为( )