The line of reflection will be x+y =4, the correct option is C.
What is the standard equation of a line?
The standard equation of a line is given by
y = mx+c
Here m is the slope and c is the y intercept
The slope can be determined by
m = (y₂ -y₁)/(x₂ -x₁)
ABCD is a square
To reflect it back to itself, it should be reflected along its diagonals
The diagonals will pass through the points A(3,1) and C( 1,3)
The slope of the line is ( 3-1)/(1-3) = 2/-2 = -1
m = -1
The equation of the line AC is
(y - y1) = m(x-x1)
It passes through the point (1,3)
(y - 3) = -1( x-1 )
y - 3 = -x +1
y +x =4
x+y =4
To known more about standard equation of a line
https://brainly.com/question/12452575
#SPJ5
