Cambridge Additional Mathematics

(singke) #1
324 Matrices (Chapter 12)

Just as the real number 0 does not have a multiplicative inverse, some matrices do not have a multiplicative
inverse. This occurs when detA=ad¡bc=0.

For the matrix A=

μ
ab
cd


:

² the value ad¡bc is called thedeterminantof matrixA, denoted detA

² if detA 6 =0, thenAisinvertibleornon-singular, and A¡^1 =

1
detA

μ
d ¡b
¡ca


² if detA=0, thenAissingular, andA¡^1 does not exist.

Example 10 Self Tutor


Find, if it exists, the inverse matrix of:

a A=

μ
56
34


b B=

μ
63
¡ 4 ¡ 2


a A=

μ
56
34


) detA= 5(4)¡6(3) = 2

) A¡^1 =^12

μ
4 ¡ 6
¡ 35


=

μ
2 ¡ 3
¡^3252


b B=

μ
63
¡ 4 ¡ 2


) detB=6(¡2)¡3(¡4)
=¡12 + 12
=0
) B¡^1 does not exist.

EXERCISE 12D.1


1aFind

μ
56
23

¶μ
3 ¡ 6
¡ 25


, and hence find the inverse of

μ
56
23


.

b Find

μ
3 ¡ 4
12

¶μ
24
¡ 13


, and hence find the inverse of

μ
3 ¡ 4
12


.

2 Find detA forAequal to:

a

μ
37
24


b

μ
¡ 13
1 ¡ 2


c

μ
00
00


d

μ
10
01


3 Find detB forBequal to:

a

μ
3 ¡ 2
74


b

μ
30
02


c

μ
01
10


d

μ
a ¡a
1 a


4 For A=

μ
2 ¡ 1
¡ 1 ¡ 1


, find:

a detA b det (¡A) c det (2A)

5 Prove that ifAis any 2 £ 2 matrix andkis a constant, then det (kA)=k^2 £detA.

cyan magenta yellow black

(^05255075950525507595)
100 100
(^05255075950525507595)
100 100 4037 Cambridge
Additional Mathematics
Y:\HAESE\CAM4037\CamAdd_12\324CamAdd_12.cdr Wednesday, 8 January 2014 11:29:37 AM BRIAN

Free download pdf