【单选题】【消耗次数：1】
数据70,71,72,73的标准差是（ ）
①
img class=kfformula src=zzximg/20190809/1565330298796439.png data-latex=\sqrt {2}/
②
img class=kfformula src=zzximg/20190809/1565330298946541.png data-latex=2/
③
img class=kfformula src=zzximg/20190809/1565330298960506.png data-latex=\frac {\sqrt {5}} {2} width=77 height=66/
④
img class=kfformula src=zzximg/20190809/1565330298247161.png data-latex=\frac {5} {3} width=84 height=70/
参考答案：
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已知img class=kfformula src=zzximg/20190809/1565322050560879.png data-latex=A\left ( {0，-2} \right )/img class=kfformula src=zzximg/20190809/1565322050489966.png data-latex=B\left ( {x，6} \right )/的中点坐标为img class=kfformula src=zzximg/20190809/1565322050782302.png data-latex=\left ( {-1，y} \right )/img class=kfformula src=zzximg/20190809/1565322050701271.png data-latex=x/img class=kfformula src=zzximg/20190809/1565322050277662.png data-latex=y/的值分别为（ ）
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img class=kfformula src=zzximg/20190809/1565322050607462.png data-latex=x=2，y=4/
②
img class=kfformula src=zzximg/20190809/1565322050205695.png data-latex=x=-2，y=2/
③
img class=kfformula src=zzximg/20190809/1565322050358526.png data-latex=x=-4，y=-2/
④
img class=kfformula src=zzximg/20190809/1565322050656212.png data-latex=x=-4，y=25/
【单选题】
在数列img class=kfformula src=zzximg/20190809/1565316783973080.png data-latex=\left \{ {{a}_{n}} \right \} /中，前img class=kfformula src=zzximg/20190809/1565316783992384.png data-latex=n/项和公式是img class=kfformula src=zzximg/20190809/1565316783683277.png data-latex={s}_{n}=4{n}^{2}-n/，那么img class=kfformula src=zzximg/20190809/1565316783325652.png data-latex={a}_{2}/为（ ）
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【单选题】
<img class="kfformula" src="20190809/1565313651838733.png" data-latex="\sqrt {7}+\sqrt {3}"/>与<img class="kfformula" src="20190809/1565313651801618.png" data-latex="\sqrt {7}-\sqrt {3}"/>的等比中项是（ ）
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<img class="kfformula" src="20190809/1565313651278262.png" data-latex="4"/>
②
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等差数列<img class="kfformula" src="20190809/1565317844150977.png" data-latex="\left \{ {{a}_{n}} \right \} "/>的首项<img class="kfformula" src="20190809/1565317844698638.png" data-latex="{a}_{1}=-2"/>，<img class="kfformula" src="20190809/1565317844536248.png" data-latex="{S}_{3}=3"/>，那么（ ）
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<img class="kfformula" src="20190809/1565317844862924.png" data-latex="d=3"/>
②
<img class="kfformula" src="20190809/1565317844935823.png" data-latex="d=2"/>
③
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【单选题】
正五棱锥的底面积是img class=kfformula src=zzximg/20190809/1565328530277328.png data-latex=26{cm}^{2}/，高是img class=kfformula src=zzximg/20190809/1565328530106797.png data-latex=6cm/，则其体积是（ ）。
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②
img class=kfformula src=zzximg/20190809/1565328531242148.png data-latex=78{cm}^{3}/
③
img class=kfformula src=zzximg/20190809/1565328531884474.png data-latex={52cm}^{3}/
④
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②
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③
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③
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120°
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②
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③
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在数列<img class="kfformula" src="20190809/1565316783973080.png" data-latex="\left \{ {{a}_{n}} \right \} "/>中，前<img class="kfformula" src="20190809/1565316783992384.png" data-latex="n"/>项和公式是<img class="kfformula" src="20190809/1565316783683277.png" data-latex="{s}_{n}=4{n}^{2}-n"/>，那么<img class="kfformula" src="20190809/1565316783325652.png" data-latex="{a}_{2}"/>为（ ）
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14
随机题目
【单选题】
变压器负载运行时，随着负载电流的增大，其铁心损耗<imgalt=""src="http://wljy.whut.edu.cn:80/uploadfiles/kindeditorAttached/image/20191205/20191205100008_669.png"/>和铜损耗<imgalt=""src="http://wljy.whut.edu.cn:80/uploadfiles/kindeditorAttached/image/20191205/20191205100015_370.png"/>会（）
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<imgalt=""src="http://wljy.whut.edu.cn:80/uploadfiles/kindeditorAttached/image/20191205/20191205095339_393.png"/>增大，<imgalt=""src="http://wljy.whut.edu.cn:80/uploadfiles/kindeditorAttached/image/20191205/20191205095346_882.png"/>不变
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③
都会增大