Precalculus with Limits: A Graphing Approach, Sixth Edition
Pw
Precalculus with Limits: A Graphing Approach, Sixth Edition View details
Review Exercises
Continue to next subchapter

Exercise 187 Page 565

We want to write the uncoded 1* 3 row matrices for the message. LOOK OUT BELOW We can start by recalling that matrix multiplication can be used to encode and decode messages. Let's recall which numbers are assigned to which letter in the alphabet. Remember that blank space corresponds to 0.

Code
0= 9=I 18=R
1=A 10=J 19=S
2=B 11=K 20=T
3=C 12=L 21=U
4=D 13=M 22=V
5=E 14=N 23=W
6=F 15=O 24=X
7=G 16=P 25=Y
8=H 16=Q 26=Z
Now, we can partition our message (including blank spaces) into groups of three. 1{\text{LOOK OUT BELOW} \\ \Updownarrow \\ L&O&O
K& &O U&T&\\  B&E&L O&W&}

Finally, we can use our table to rewrite each group as a 1* 3 matrix.

Group of Three Letters Uncoded Row Matrix
L&O&O 12&15&15
K& &O 11&0&15
U&T& 21&20&0
B&E&L 2&15&12
O&W& 15&23&0
First, we can look at the given encoding matrix. 2&-2 & 0 3&0&- 3 - 6& 2&3 We want to encode the message from Part A using the given encoding matrix. Let's consider the uncoded row matrices from Part A! 1{12&15&15 11&0&15 21&20&0
\\ 2&5&12 15&23&0}
Now, we can multiply each of the uncoded row matrices by the encoding matrix to get a corresponding coded matrices. Let's start with the first uncoded row matrix.
12& 15 & 15 2&-2 & 0 3&0&- 3 - 6& 2&3
12(2)+ 15(3)+ 15(- 6) & 12(- 2)+ 15(0)+ 15(2) & 12(0)+ 15(- 3)+ 15(3)
24+45+(- 90) & - 24+0+30 & 0+(- 45)+45
24+45-90 & - 24+0+30 & 0- 45+45
- 21 & 6&0
Now, we can do the same for the second uncoded row matrix.
11& 0 & 15 2&-2 & 0 3&0&- 3 - 6& 2&3
11(2)+ 0(3)+ 15(- 6) & 11(- 2)+ 0(0)+ 15(2) & 11(0)+ 0(- 3)+ 15(3)
22+0+(- 90) & - 22+0+30 & 0+0+45
22+0-90 & - 22+0+30 & 0+0+45
- 68 & 8&45
Next, we can encode the third row matrix in a similar fashion.
21& 20 & 0 2&-2 & 0 3&0&- 3 - 6& 2&3
21(2)+ 20(3)+ 0(- 6) & 21(- 2)+ 20(0)+ 0(2) & 21(0)+ 20(- 3)+ 0(3)
42+60+0 & - 42+0+0 & 0+(- 60)+0
42+60+0 & - 42+0+0 & 0-60+0
102 & - 42&- 60
Next, we can encode the third row matrix in a similar fashion.
2& 5 & 12 2&-2 & 0 3&0&- 3 - 6& 2&3
2(2)+ 5(3)+ 12(- 6) & 2(- 2)+ 5(0)+ 12(2) & 2(0)+ 5(- 3)+ 12(3)
4+15+(- 72) & - 4+0+24 & 0+(- 15)+36
4+15-72 & - 4+0+24 & 0-15+36
- 53 & 20& 21
Finally, we can encode the last row matrix!
15& 23 & 0 2&-2 & 0 3&0&- 3 - 6& 2&3
15(2)+ 23(3)+ 0(- 6) & 15(- 2)+ 23(0)+ 0(2) & 15(0)+ 23(- 3)+ 0(3)
30+69+0 & - 30+0+0 & 0+(- 69)+0
30+69+0 & - 30+0+0 & 0-69+0
99 & - 30&- 69
Now, we can list the sequence of coded row matrices. - 21&6&0 - 68&8&45 102&- 42&- 60 - 53&20&21 99&- 30&- 69 Finally, we can remove the matrix notation and write the cryptogram corresponding to our message. - 21 6 0 - 68 8 45 102 - 42 - 60 - 53 20 21 99 - 30 - 69 We encoded our message!