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A First Course in Linear Algebra, 2017a

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5.2. The Matrix of a L<strong>in</strong>ear Transformation I 275<br />

⎡<br />

T ⎣<br />

0<br />

−1<br />

2<br />

⎤<br />

⎦ =<br />

⎡<br />

⎣<br />

1<br />

3<br />

−1<br />

⎤<br />

⎦<br />

F<strong>in</strong>d the matrix of T. That is f<strong>in</strong>d A such that T(⃗x)=A⃗x.<br />

Exercise 5.2.7 Suppose T is a l<strong>in</strong>ear transformation such that<br />

⎡<br />

T ⎣<br />

⎤<br />

1<br />

2 ⎦ =<br />

⎡ ⎤<br />

5<br />

⎣ 2 ⎦<br />

−18 5<br />

⎡<br />

T ⎣<br />

⎡<br />

T ⎣<br />

−1<br />

−1<br />

15<br />

0<br />

−1<br />

4<br />

⎤<br />

⎦ =<br />

⎤<br />

⎦ =<br />

F<strong>in</strong>d the matrix of T. That is f<strong>in</strong>d A such that T(⃗x)=A⃗x.<br />

⎡<br />

⎣<br />

⎡<br />

⎣<br />

3<br />

3<br />

5<br />

⎤<br />

⎦<br />

2<br />

5<br />

−2<br />

⎤<br />

⎦<br />

Exercise 5.2.8 Consider the follow<strong>in</strong>g functions T : R 3 → R 2 . Show that each is a l<strong>in</strong>ear transformation<br />

and determ<strong>in</strong>e for each the matrix A such that T(⃗x)=A⃗x.<br />

⎡<br />

(a) T ⎣<br />

⎡<br />

(b) T ⎣<br />

⎡<br />

(c) T ⎣<br />

⎡<br />

(d) T ⎣<br />

x<br />

y<br />

z<br />

x<br />

y<br />

z<br />

x<br />

y<br />

z<br />

x<br />

y<br />

z<br />

⎤<br />

⎦ =<br />

⎤<br />

⎦ =<br />

⎤<br />

⎦ =<br />

⎤<br />

⎦ =<br />

[ x + 2y + 3z<br />

2y − 3x + z<br />

]<br />

[ 7x + 2y + z<br />

3x − 11y + 2z<br />

[<br />

3x + 2y + z<br />

x + 2y + 6z<br />

[ 2y − 5x + z<br />

x + y + z<br />

]<br />

]<br />

]<br />

Exercise 5.2.9 Consider the follow<strong>in</strong>g functions T : R 3 → R 2 . Expla<strong>in</strong> why each of these functions T is<br />

not l<strong>in</strong>ear.<br />

⎡<br />

(a) T ⎣<br />

x<br />

y<br />

z<br />

⎤<br />

⎦ =<br />

[ x + 2y + 3z + 1<br />

2y − 3x + z<br />

]

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