In: Advanced Math
Let V be a vector space, and suppose that U and W are both subspaces of V. Show that U ∩W := {v | v ∈ U and v ∈ W} is a subspace of V.
Defination : Let V be a vector space , a subset A V is said to be a subspace of V if the following two conditions are hold
(i) x € A and y € A then x +y € A
(ii) x € A and c be a constant then cx € A.
Now given U and W both are subspace of V .
(i) Let x € U W .
Then x € U and x€ W . Now since both U and W are subspace of V so x + y belongs to both U and V .
This implies x + y € U W . So x € U W and y € U W implies x + y belongs to U W .
So condition (i) satisfies .
(ii) Suppose x € U W and c be a scalar .
Since x € U W so x € U and x € W .
Now as both U and W are subspace of V then ,
cx € U and cx € Y => cx € U W .
So x € U W and c be a scalar implies cx € U W .
So condition (ii) satisfies .
Hence U W is a subspace of V .