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buckaroobill
04-08-2007, 09:55 PM
The following proof was confusing me so any help would be appreciated!

Let V be a vector space and let W_1 and W_2be subspaces of V. Prove that W_1 \cap W_2 is a subspace of V. (Do not forget to show that W_1 \cap W_2 is nonempty.)

daon
04-09-2007, 01:27 AM
If a,b are in the intersection, then a,b are in W1 and a,b are in W2. Therefore a+b must also be in W1,W2, so it lies in the intersection. Let k be a scalar and v be a vector in the intersection of W1,W2. Then v is in W1 and v is in W2, and so kv is in W1, W2 and hence it also lies in the intersection. It is nonempty because the zero vector for V is in any subspace of V, so it must be in the intersection of any set of subspaces from V.