端木·宇 2008-6-19 20:35
Vector Subtraction
---You probably know that subtraction is the same thing as adding anegative: 8 – 5 is the same thing as 8 + (–5). The easiest way to thinkabout vector subtraction is in terms of adding a negative vector.What’s a negative vector? It’s the same vector as its positivecounterpart, only pointing in the opposite direction.
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[i][b] A[/b][/i] – [i][b]B[/b][/i], then, is the same thing as [i][b]A[/b][/i] + (–[i][b]B[/b][/i]). For instance, let’s take the two vectors [i][b]A[/b][/i] and [i][b]B[/b][/i]:
[align=center][img]http://www.24en.com/d/file/sat/sat2/physics/2008-01-24/01bd0da7bf86227526f8251f7335f39e.gif[/img][/align]
To subtract [i][b]B[/b][/i] from [i][b]A[/b][/i], take a vector of the same magnitude as [i][b]B[/b][/i], but pointing in the opposite direction, and add that vector to[i][b] A[/b][/i], using either the tip-to-tail method or the parallelogram method.
[align=center][img]http://www.51sat.net/Article/UploadFiles/200709/20070911151040622.gif[/img][/align]
