Math 2406: Abstract Vector Spaces

Lecture 7 Plan  (Tuesday, September 11, 2007).

Apostol 3.11-3.12.

Today we add an important ingredient to a linear space: an inner product, the generalization of a dot product for vectors.  The inner product allows us to generalize our concept of length and angle, so we can talk about the "norm" of a function, and two functions being "orthogonal".  Since the inner product allows us to measure things in a linear space, we call the pair (linear space, inner product) a metric space.

Review questions:

1. Would the inner product in example 2, p. 104, continue to be an inner product if the second term were x_1*x_2?
2. In example 4, p. 105, what goes wrong if the weight function is w(t) = sin(t)?
3. Is it true that if a function f is orthogonal to a constant function on any fixed interval, then f has zero mean on that interval?



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