Math Arguments

Complicated Crossings.

Explain WHY this works for adding fractions.




Three very similar-looking, but very different, ideas.
Which of these apply here?
Which don't?

The Butterfly, aka., "Cross-Adding".
Cross-canceling.
Cross-multiplying.

Now that you've explored the WHY of this trick, do you still want to continue using it or will you use another method?

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