【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( )
①
<img class="kfformula" src="20190809/1565313651278262.png" data-latex="4"/>
②
<img class="kfformula" src="20190809/1565313651577788.png" data-latex="\pm 4"/>
③
<img class="kfformula" src="20190809/1565313651689008.png" data-latex="\pm 2"/>
④
<img class="kfformula" src="20190809/1565313651298877.png" data-latex="2"/>
【单选题】
若x+y=1,则x与y的等差中项是()
①
img src=zzximg/20190822/1566466219602205.png title=1566466219602205.png alt=图片3.png/
②
img src=zzximg/20190822/1566466227823753.png title=1566466227823753.png alt=图片4.png/
③
img src=zzximg/20190822/1566466134821449.png title=1566466134821449.png alt=图片1.png/
④
img src=zzximg/20190822/1566466168502672.png title=1566466168502672.png alt=图片2.png/