---What's the matter with Tim?---Oh, Tim's cellphone was left in a taxi accidentally, never _____again.    

 

A. to find    B. to be found    C. finding    D. being found    

 

             

Work hard, and you will (success). Work hard, and you will (success).

测定铅锡合金中Pb、Sn含量时,称取试样0.2000g,用盐酸溶解后,准确加入50.00mL 0.03000mol/L的EDTA,50mL水,加热煮沸2min,

化简：. 化简：.

设Z1,Z2,Z3三点适合条件：Z1+Z2+Z3=0及|Z1|=|Z2|=|Z3|=1试证明Z1.Z2.Z3是内接于单位圆周|Z|=1的 正三角形的顶点.

设A是n阶矩阵,满足 ,则 _____. 设A是n阶矩阵,满足 ,则 _____.

计算,其中是从点A(3,2,1)到点B(0,0,0)的直线段AB. 计算,其中是从点A(3,2,1)到点B(0,0,0)的直线段AB.

设矩阵A= ,E为2阶单位矩阵,矩阵B满足BA=B+2E,则|B|=_____. 设矩阵A= ,E为2阶单位矩阵,矩阵B

已知 , , 是某二阶常系数非齐次线性微分方程的3个解,则该方程满足条件 的解为y= ________ .