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Matrices and Determinants 7.33<br />

4. We have,<br />

X 2 5 3 6<br />

+ Ê ˆ Ê ˆ<br />

Á =<br />

Ë3 -2 ˜<br />

¯<br />

Á<br />

Ë2 7<br />

˜<br />

¯<br />

fi<br />

fi<br />

5. Clearly,<br />

fi<br />

and<br />

fi<br />

X 3 6 2 5<br />

= Ê ˆ Ê ˆ<br />

Á -<br />

Ë2 7<br />

˜<br />

¯<br />

Á<br />

Ë3 -2<br />

˜<br />

¯<br />

X 1 1<br />

= Ê ˆ<br />

Á<br />

Ë-1 9 ˜<br />

¯<br />

1 ÊÊ2 5 ˆ Ê4 2 ˆˆ<br />

X =<br />

2 ÁÁ +<br />

3 2<br />

˜ Á<br />

8 2<br />

˜<br />

ËË - ¯ Ë - ¯˜<br />

¯<br />

1 Ê 6 7 ˆ Ê 3 7/2ˆ<br />

X =<br />

2<br />

Á =<br />

Ë11 -4 ˜<br />

¯<br />

Á<br />

Ë11/2 -2<br />

˜<br />

¯<br />

1 ÊÊ2 5 ˆ Ê4 2 ˆˆ<br />

Y =<br />

2 ÁÁ -<br />

3 2<br />

˜ Á<br />

8 2<br />

˜<br />

ËË - ¯ Ë - ¯˜<br />

¯<br />

1 Ê-2 3ˆ Ê -1 3/2ˆ<br />

Y =<br />

2<br />

Á =<br />

Ë-5 0<br />

˜<br />

¯<br />

Á<br />

Ë-5/2 0<br />

˜<br />

¯<br />

6. Given A + 2B + X = O<br />

fi X = –(A + 2B)<br />

ÊÊ2 -1ˆ Ê-1 1ˆˆ<br />

=- Á + 2<br />

Ë<br />

Á<br />

Ë3 5˜ ¯<br />

Á<br />

Ë 0 2˜<br />

¯˜<br />

¯<br />

ÊÊ2 -1ˆ Ê-2 2ˆˆ<br />

=- Á +<br />

Ë<br />

Á<br />

Ë3 5˜ ¯<br />

Á<br />

Ë 0 4˜<br />

¯˜<br />

¯<br />

Ê0 1ˆ Ê 0 -1ˆ<br />

=- Á =<br />

Ë3 9˜ ¯<br />

Á<br />

Ë-3 -9˜<br />

¯<br />

Ê<br />

7. Given || x 2 ˆ Ê<<br />

3 2 ˆ<br />

Á =<br />

Ë 5 | y - 2|<br />

˜<br />

¯<br />

Á<br />

Ë 5 < 4<br />

˜<br />

¯<br />

fi |x| < 2, |y – 2| < 3<br />

fi –2 < x < 2, –3 < (y – 2) < 3<br />

fi –2 < x < 2, –1 < y < 5<br />

8. We have<br />

Ê<br />

3<br />

x - 3x+ 2 2 ˆ Ê0 2ˆ<br />

Á<br />

3 2<br />

˜ = Á<br />

3 y 7y<br />

35 Ë3 1<br />

˜<br />

Ë<br />

+ - ¯ ¯<br />

x 3 – 3x + 2 = 0, y 3 + 7y 2 – 35 = 1<br />

x 3 – 3x + 2 = 0, y 3 + 7y 2 – 36 = 1<br />

Now, x 3 – 3x + 2 = 0<br />

fi x 3 – x 2 + x 2 – x – 2x + 2 = 1<br />

fi x 2 (x – 1) + x(x – 1) – 2(x – 1) = 0<br />

fi (x – 1)(x 2 + x – 2) = 0<br />

fi (x – 1)(x + 2)(x – 1) = 0<br />

fi (x – 1) 2 (x + 2) = 0<br />

fi x = 1, –2<br />

Also, y 3 + 7y 2 – 36 = 0<br />

fi y 3 – 2y 2 + 9y 2 – 18y + 18y – 36 = 1<br />

fi y 2 (y – 2) + 9y(y – 2) + 18(y – 2) = 0<br />

fi (y – 2)(y 2 + 9y + 18) = 0<br />

fi (y – 2)(y + 3)(y + 6) = 0<br />

fi y = 2, –3, –6<br />

Thus,<br />

S(x + y) = (1 – 2 + 2 – 3 – 6) = –8<br />

9. We have<br />

Êx<br />

yˆ Ê1 -2ˆ Ê3 5ˆ<br />

2Á + 3 = 4<br />

Ëz<br />

t<br />

˜<br />

¯<br />

Á<br />

Ë0 4<br />

˜<br />

¯<br />

Á<br />

Ë4 6<br />

˜<br />

¯<br />

Êx<br />

yˆ Ê3 5ˆ Ê1 -2ˆ<br />

fi 2Á = 4 -3<br />

Ëz<br />

t<br />

˜<br />

¯<br />

Á<br />

Ë4 6<br />

˜<br />

¯<br />

Á<br />

Ë0 4<br />

˜<br />

¯<br />

fi<br />

Ê2x<br />

2yˆ Ê12 20ˆ Ê3 -6ˆ<br />

Á = -<br />

Ë2z<br />

2t<br />

˜<br />

¯<br />

Á<br />

Ë16 24<br />

˜<br />

¯<br />

Á<br />

Ë0 12<br />

˜<br />

¯<br />

Ê 9 26ˆ<br />

= Á<br />

Ë16 12 ˜<br />

¯<br />

fi x = 9/2, y = 13, z = 8, t = 6<br />

10. Let<br />

Ê2 3ˆ Ê-1 2 ˆ<br />

A= Á and B=<br />

Ë4 0<br />

˜<br />

¯<br />

Á<br />

Ë 1 -5<br />

˜<br />

¯<br />

Solving, we get<br />

1 1<br />

X = (3B - 2 A) and Y = (3A-2 B)<br />

5 5<br />

1 ÊÊ-3 6 ˆ Ê4 6ˆˆ<br />

Thus, X =<br />

5 ÁÁ -<br />

3 15<br />

˜ Á<br />

8 0<br />

˜<br />

ËË - ¯ Ë ¯˜<br />

¯<br />

fi<br />

and<br />

fi<br />

11. Given<br />

1 Ê-7 0 ˆ Ê-7/5 0 ˆ<br />

X =<br />

5<br />

Á =<br />

Ë-5 -15 ˜<br />

¯<br />

Á<br />

Ë -1 -3<br />

˜<br />

¯<br />

1 ÊÊ 6 9ˆ Ê-2 4 ˆˆ<br />

Y =<br />

5 ÁÁ -<br />

12 0<br />

˜ Á<br />

2 10<br />

˜<br />

ËË ¯ Ë - ¯˜<br />

¯<br />

1 Ê 8 5ˆ Ê8/5 1ˆ<br />

Y =<br />

5<br />

Á =<br />

Ë10 10<br />

˜<br />

¯<br />

Á<br />

Ë 2 2<br />

˜<br />

¯<br />

Ê2 0ˆ<br />

A = Á<br />

Ë0 2 ˜<br />

¯<br />

Ê1 0ˆ<br />

= 2Á<br />

= 2I<br />

Ë0 1<br />

˜<br />

¯<br />

We have,<br />

f(x) = 1 + x + x 2 + … to<br />

1<br />

=<br />

1 - x<br />

fi<br />

I<br />

f( A)<br />

=<br />

I - A<br />

I<br />

=<br />

I - 2I<br />

I<br />

=-<br />

I<br />

2<br />

I<br />

=-<br />

I<br />

=-I

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