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enter image description here

I can't seem to identify what the arrows are indicating in this question, obviously the two lines are parallel but what does it mean? I don't know where to begin.

Any suggestions?

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    $\begingroup$ One of the common tangents is the $x$-axis. $\endgroup$ – André Nicolas Apr 13 '15 at 21:01
  • $\begingroup$ Ah! I see, thank you all $\endgroup$ – IAmAlfred Apr 13 '15 at 21:19
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The arrows pointing to lines in that manner is commonly used in technical drawing when you want to write down the numerical value of a distance in a location that's not adjacent to the geometric entity it refers to.

Since the lines are parallel and the distance between the lines is 8cm, that means the distance between the circles along that direction is also 8cm. That is the entire purpose of those lines; they are not a part of the "actual" diagram.

Here is another example of such notation, to show that the given circle has diameter 10:

enter image description here

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The two arrows are simply pointing to something. They are not vectors,or directions, etc. They are pointing to the lines indicating distance.

For example, there is 8cm distance between the two circles. Otherwise, just ignore the two "parallel lines." They are not actually part of the "diagram".

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