Which of the following are subspaces of R3 ?(i) {(x,y,z)| z = 2x+3y+2}(ii) {(x,y,z)| x2+y2=z2}Select one:a. (ii) onlyb. (i) and (ii)c. None of the other choices is correctd. (i) only
Question
Which of the following are subspaces of R3 ?(i) {(x,y,z)| z = 2x+3y+2}(ii) {(x,y,z)| x2+y2=z2}Select one:a. (ii) onlyb. (i) and (ii)c. None of the other choices is correctd. (i) only
Solution
A subspace of R3 must satisfy three conditions:
- The zero vector is in the subspace.
- The subspace is closed under vector addition.
- The subspace is closed under scalar multiplication.
Let's check these conditions for both options:
(i) {(x,y,z)| z = 2x+3y+2}
- The zero vector (0,0,0) is not in this set because if x=y=0, then z=2 which is not zero.
- & 3. Even if we check these, the first condition is not met, so this is not a subspace.
(ii) {(x,y,z)| x^2 + y^2 = z^2}
- The zero vector (0,0,0) is in this set because if x=y=z=0, the equation holds.
- The set is not closed under addition. For example, (1,0,1) and (0,1,1) are in the set, but their sum (1,1,2) is not.
- The set is not closed under scalar multiplication. For example, (1,0,1) is in the set, but its double (2,0,2) is not.
So, neither (i) nor (ii) is a subspace of R3. Therefore, the correct answer is c. None of the other choices is correct.
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