当a=5时,a2+2a的运算结果是( )
A.20
B.35
C.50
D.100
当a=5时,
a2+2a
=52+2×5,
=25+10
=35.
故选:B.
Animals are part of nature should be well protected.
A. and B. or C. but
两样本均数差别的假设检验用t检验的条件是()
A.两总体均数相等
B.两总体方差相等
C.两样本均为大样本
D.两样本均为小样本
E.两总体均符合正态分布