Question

Which of the following matrices would be used in matrix multiplication to find the reflection about the line y = -x?
Answer
A. -1, 0
0,-1
B. 1,0
0-1
C. 0,1
1,0
D. 0,-1
-1,0

Answer 1

Why not try them out on some examples, say
0,-1 which should be reflected into ..

Answer 2

Or even 1,1

Answer 3

What is A times <1,1> ?

Answer 4

any given point would be defined as (x,-x) ... is my idea

Answer 5

As opposed to just doing trials.

Answer 6

i like trials too :)

Answer 7

Anyhow, the point is that A times <1,1> works as you want, the other three do not.
Confirm with another couple examples.

Answer 8

A does not work ....

Answer 9

i think its B

Answer 10

B is good

Answer 11

is that the right answer?

Answer 12

ugh, i seen it wrong ;/

Answer 13

oh

Answer 14

A times <1,1> is <-1,-1> which is a correct reflection across y = -x???

Answer 15

telliot is correct :)