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A First Course in Linear Algebra, 2017a

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9.1. <strong>Algebra</strong>ic Considerations 455<br />

• We wish to show that a(b⃗x)=(ab)⃗x.<br />

⎛ ⎡<br />

a(b⃗x) = a⎜<br />

⎝ b ⎢<br />

⎣<br />

⎛⎡<br />

= a⎜⎢<br />

⎝⎣<br />

=<br />

=<br />

⎡<br />

⎢<br />

⎣<br />

⎡<br />

⎢<br />

⎣<br />

⎤<br />

x 1<br />

x 2<br />

⎥<br />

. ⎦<br />

x n<br />

⎤<br />

bx 1<br />

bx 2<br />

⎥<br />

. ⎦<br />

bx n<br />

a(bx 1 )<br />

a(bx 2 )<br />

.<br />

a(bx n )<br />

= (ab) ⎢<br />

⎣<br />

⎤<br />

⎥<br />

⎦<br />

⎤<br />

(ab)x 1<br />

(ab)x 2<br />

⎥<br />

. ⎦<br />

(ab)x n<br />

⎡<br />

= (ab)⃗x<br />

⎤<br />

x 1<br />

x 2<br />

⎥<br />

. ⎦<br />

x n<br />

⎞<br />

⎟<br />

⎠<br />

⎞<br />

⎟<br />

⎠<br />

• F<strong>in</strong>ally, we need to show that 1⃗x =⃗x.<br />

⎡<br />

1⃗x = 1⎢<br />

⎣<br />

=<br />

=<br />

⎡<br />

⎢<br />

⎣<br />

⎡<br />

⎢<br />

⎣<br />

= ⃗x<br />

⎤<br />

x 1<br />

x 2<br />

⎥<br />

. ⎦<br />

x n<br />

⎤<br />

1x 1<br />

1x 2<br />

⎥<br />

. ⎦<br />

1x n<br />

⎤<br />

x 1<br />

x 2<br />

⎥<br />

. ⎦<br />

x n<br />

By the above proofs, it is clear that R n satisfies the vector space axioms. Hence, R n is a vector space<br />

under the usual operations of vector addition and scalar multiplication.<br />

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