In the Real World Examples Page 1

The perimeter P of a rectangle with length l and width w is given by P = l + l + w + w. How can this formula be better expressed?

If we used this version of the formula, we would need to add l + l and w + w every time we performed a substitution. It is more efficient to use the formula P = 2l + 2w. This way we have already added l + l and w + w. It occupies less space and kills fewer trees, and we are less likely to need to deal with something like what Mark Wahlberg went through in The Happening. Did you see that movie? That was terrifying. That a film that awful could be produced by a major studio. Chills.