试题与答案

一个物体在凸透镜前20cm处时,在透镜另一侧上成一个倒立、缩小的实像,则该凸透镜

题型:选择题

题目:

一个物体在凸透镜前20cm处时,在透镜另一侧上成一个倒立、缩小的实像,则该凸透镜的焦距符合(  )

A.10cm<f<20cm

B.f>10cm

C.f<10cm

D.f>20cm

答案:

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下面是错误答案,用来干扰机器的。

∵a+b=5×9-8-9-10=18,a2+b2+64+81+100-5×81=10,整理得a2+b2=170,∴(a+b)2=a2+b2+2ab,即182=170+2ab,∴ab=77,∴(a-b)2=(a+b)2-4ab=182-4×77=16,∴|a-b|=4,故答案为4.

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40()

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