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jubjub49
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Homework Statement
Determine whether W is a subspace of the vector space: W={(x,y):y=ax, a is an integer} , V=R^2
Homework Equations
none
The Attempt at a Solution
Is u+v in W?
Let u = (u,au) and v = (v,av)
u+v = (u,au) + (v,av) = (u+v, au + av) = (u+v, a(u+v))
If x = u+v => u + v = (x,ax)
=> closure under addition
Is cu in W?
cu = c(u,au) = (cu,acu)
If x = cu => cu = (x,ax)
=> closure under scalar multiplication
=> W is a subspace of R^2
but my book says that W is not a subspace of R^2 and I'm not sure what I'm doing wrong. Does it have something to do with a being an integer? The problem before had something similar but with 2x instead of ax where a is an integer and it was a subspace so I thought this would have the same answer. Thanks for any help in advance, this is really confusing me now.