- #1
trap101
- 342
- 0
V is the direct sum of W1 and W2 in symbols:
V = W1 (+) W2 if:
V = W1 + W2 and
W1 [itex]\cap[/itex] W2 = {0}
Show that the following statements are equivalent:
1. V = W1 (+) W2
2. Every vector v[itex]\in[/itex]V can be written uniquely as w1 + w2 where w1[itex]\in[/itex]W1 and w2[itex]\in[/itex]W2
3. V = W1 + W2 and for vectors w1[itex]\in[/itex]W1 and w2[itex]\in[/itex]W2 if w1 +w2 = 0 then w1 = w2
4. If [itex]\alpha[/itex]1 is a basis for W1 and [itex]\alpha[/itex]2 is a basis for W2 then
[itex]\alpha[/itex] = [itex]\alpha[/itex]1 [itex]\cup[/itex] [itex]\alpha[/itex]2
Attempt:
I'm thrown off here because I'm given the definition of a direct sum. So how can I even show that all these statements are equivalent? Would I start by assuming one of the statements is true? For example: Let's say statement 1 is true. that means...well it means exactly what statement 2 is. Maybe take a vector in W1 and one in W2 sum them together and create a vector in V? But then to do that I would have to define an exact vector space...
V = W1 (+) W2 if:
V = W1 + W2 and
W1 [itex]\cap[/itex] W2 = {0}
Show that the following statements are equivalent:
1. V = W1 (+) W2
2. Every vector v[itex]\in[/itex]V can be written uniquely as w1 + w2 where w1[itex]\in[/itex]W1 and w2[itex]\in[/itex]W2
3. V = W1 + W2 and for vectors w1[itex]\in[/itex]W1 and w2[itex]\in[/itex]W2 if w1 +w2 = 0 then w1 = w2
4. If [itex]\alpha[/itex]1 is a basis for W1 and [itex]\alpha[/itex]2 is a basis for W2 then
[itex]\alpha[/itex] = [itex]\alpha[/itex]1 [itex]\cup[/itex] [itex]\alpha[/itex]2
Attempt:
I'm thrown off here because I'm given the definition of a direct sum. So how can I even show that all these statements are equivalent? Would I start by assuming one of the statements is true? For example: Let's say statement 1 is true. that means...well it means exactly what statement 2 is. Maybe take a vector in W1 and one in W2 sum them together and create a vector in V? But then to do that I would have to define an exact vector space...