Help proving a subset is a subspace

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SUMMARY

The set of all 3-vectors orthogonal to the vector [1, -1, 4] forms a subspace of R^3. This is established by demonstrating that any vector in this set satisfies the equation a - b + 4c = 0. To prove closure under vector addition and scalar multiplication, one must show that if v_1 and v_2 are both orthogonal to [1, -1, 4], then (v_1 + v_2) is also orthogonal to [1, -1, 4] using the distributive property of the dot product.

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Homework Statement



Prove that the set of all 3-vectors orthogonal to [1, -1, 4] forms a subspace of R^3.

Homework Equations



Orthogonal means dot product is 0.

The Attempt at a Solution



I know the vectors in this subspace are of the form
[a,b,c] where a - b + 4c = 0.
However I don't know how to use this to show there is closure under vector addition and scalar multiplication.
 
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Let v_1 and v_2 be two vectors orthogonal to the given vector (call it a), i.e.

[tex]v_1 \cdot a = 0[/tex]
[tex]v_2 \cdot a = 0[/tex]

Now, using these, all you have to do is show that

[tex](v_1 + v_2) \cdot a = 0[/tex]

HINT: Use distributivity of the dot product.
 

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