Mathematics Weblog
Some textbooks misuse infinity
Monday 18 October 2004 at 3:43 pm | In Articles | Post CommentIt’s happened again! used in a textbook (unnamed to protect the guilty) as if it were a real number instead of an idea. In a discussion of the formula for the acute angle between two lines
the following appears:
- Putting gives an angle , confirming the condition for the lines to be perpendicular
This is of course complete nonsense. As I’ve said before doesn’t exist and is only defined on ie for
The textbook was written by the examiners (which is one reason why we use it); this worries me even more.
I suppose this is better than one well-known textbook back in the eighties which solved the equation by putting then ‘showing’ or . This seems to show that all linear equations are quadratics in disguise; or cubics, quartics – who knows where this nonsense leads 😕
See also Division by zero shock!
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