Circle p is tangent to the x axis and the y axis. if the coordinates ofthe center are (r, r) find the equation of the line containing the points of tangency a) x + y= r b) x-y=r c) x+y=1

We know that
Circle p is tangent to the x axis and the y axis
so
the point in the x axis is (0,r)
the point in the y axis is (r,0)

the equation of the line that containing the points of tangency is
point A(0,r)  point B(r,0)
m=(y2-y1)/(x2-x1)> m=(0-r)/(r-0)> m=-r/r> m=-1

with
m=-1  and point A(0,r)
y-y1=m(x-x1)> y-r=-1*(x-0)> y=-x+r> y+x=r

the answer is the option
A) x + y= r