There is a typo. One which obfuscates the main point and makes it difficult for anyone unfamiliar with the problem to deduce the answer.

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  • $\begingroup$ The x and arrow to the right that looks like a graph axis seems out of place. $\endgroup$
    – M. Enns
    Apr 14, 2016 at 17:06
  • $\begingroup$ No, that's fine, it's the x-axis. $\endgroup$ Apr 14, 2016 at 17:06
  • 2
    $\begingroup$ And your point is what? This is one specific diagram from one specific book. Doesn't belong here, IMO. $\endgroup$
    – Bill N
    Apr 14, 2016 at 21:33
  • 4
    $\begingroup$ I'm voting to close this question as off-topic because its not about a concept in physics. It's just a challenge to spot an error in a diagram from a book. $\endgroup$ Apr 15, 2016 at 7:52

1 Answer 1


The angles XCF and N'CB are marked as being the same angle, but that is clearly nonsense since that would makes line CB parallel to line FB.

  • $\begingroup$ It would make CB perpendicular to CF (which they are), I don't see the problem since one can clearly see relative to what lines the angles are defined. $\endgroup$
    – Yukterez
    Apr 14, 2016 at 18:55
  • $\begingroup$ In the triangle CBF the diagram as shown does indeed have CB perpendicular to CF, as is BF. So apparently the three angles in the triangle are $90^\circ $, $90^\circ $ and zero. $\endgroup$
    – PhillS
    Apr 14, 2016 at 19:02
  • $\begingroup$ You got it. The wrong angle is marked as 90 degrees. The right angle is BCF not CFB. $\endgroup$ Apr 14, 2016 at 19:39

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