0 votes 0 votes 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 Linear Algebra vector-space engineering-mathematics + – srestha asked May 17, 2018 srestha 451 views answer comment Share Follow See all 3 Comments See all 3 3 Comments reply Kushagra Chatterjee commented May 17, 2018 reply Follow Share 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. 1 votes 1 votes srestha commented May 17, 2018 reply Follow Share ok but the space should be in 2D how they consider 1D line as space? 0 votes 0 votes Kushagra Chatterjee commented May 17, 2018 reply Follow Share Why the space should be in 2D 0 votes 0 votes Please log in or register to add a comment.