Dash Dash The dash is a punctuation mark that is similar in appearance to and , but differs from these symbols in both length and height. The most common versions of the dash are the en dash (–), equal to half the height of the font; the em dash (—), twice as long as the en dash; and the horizontal bar (―), whose length varies across typefaces. Historically, the names of en dash and em dash were loosely related to the width of a lower-case "n" and upper-case "M", respectively, in commonly used typefaces. Usage varies both within English and in
Chain rule for short, The derivative function is therefore: Another way of computing this derivative is to view the composite function as the composite of and "h". Applying the chain rule to this situation gives: This is the same as what was computed above. This should be expected because . Sometimes it is necessary to differentiate an arbitrarily long composition of the form formula_23. In this case, define where formula_25 and formula_26 when formula_27. Then the chain rule takes the form or, in the Lagrange notation, The chain rule can be used to derive some well-known differentiation rules. For example, the quotient