The image of the point (1, -2) after a rotation of 180° about the origin is

Answer 1

(-1,+2) by inspection

using 90 deg matrix
R90 =
|+0 -1|
|+1 +0|
R180 is R90 * R90
|+0 -1||+0 -1|
|+1 +0||+1 +0|
which is
|-1 +0|
|+0 -1|

Answer 2

|-1 +0| |+1|
|+0 -1| |-2|

= (-1, +2 )