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【简答题】
已知a、b是非零向量，指出下列等式成立的条件： ①|a|+|b|=|a+b|成立的条件是______； ②|a|+|b|=|a-b|成立的条件是______； ③|a+b|=|a-b|成立的条件是______； ④|a|-|b|=|a-b|成立的条件是______．
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【简答题】 在单相桥式整流电路中,变压器次级电压 V 2 =120V (见下图),在未接滤波电容 C 时负载两端电压 V L 是多少伏?加了滤波电容并在空载情况下输出的直流电压最大值可达多少伏,此时整流二极管实际承受的反向电压是多大?
【单选题】The example of the man shows an ability to ______.
A.
avoid traffic accidents
B.
judge the good and evil of a person
C.
know about the events that are happening some distance away
D.
sense a danger that will actually happen later on
【单选题】在单相桥式整流、电容滤波电路中，下列说法正确的是（ ）。【图片】
A.
二极管承受反向电压最大值为输入电压的最大值
B.
若电容为电解电容，其极性应与输出电压极性相反
C.
电路输出电压的最大值为输入电压的有效值
D.
当电容C开路时，各二极管的导通角不变
【简答题】肘关节的关节面有三对,包括:_______、________和_______。
【简答题】What do most parents expect of their children in preschools? A) The ability to get along with other children B) The to learn what they like C) Enjoyment of free play D) Good academic performan...
【简答题】A．The ability to read different books in different ways. B．The ability to think actively in reading. C．The ability to raise and answer questions. D．The ability to read quickly.
【简答题】A．It can affect the ability of finding information. B．It decides the ability of reading newspaper. C．It can affect the ability to earn a living. D．It decides the pleasure of reading.
【单选题】A set of genes play a role in learning to read and do math, but this ability is not just gene-driven,【C1】______schooling and help from parents are also vital【C2】______. Early mathematical ability and ...
A.
as
B.
so
C.
though
D.
if
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