Vector

Question

https://www.youtube.com/watch?v=3SkCNpFOshk

In this lecture , can somebody define in 2nd question why $X_{1}+X_{2}\notin V_{1}\cup V_{2}$?

I cannot understand the proof

Comments

The union of two linear spaces generated by X1 and X2 is the two lines shown in the video.

But X1 + X2 does not lie any of these two lines thats why it does not belong to the union of two linear spaces.

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ok

but the space should be in 2D

how they consider 1D line as space?

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Why the space should be in 2D