Exercise 3.1.30

Answers

(a)
If u and v are both in S + T, then u = s1 + t1 and v = s2 + t2. So u + v = (s1 + s2) + (t1 + t2) is also in S + T. And so is cu = cs1 + ct1 : S + T = subspace.
(b)
If S and T are different lines, then S T is just the two lines (not a subspace) but S + T is the whole plane that they span.
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2022-01-16 13:28
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