Circle is graphed in the coordinate plane with the equation x2 + y2 = 81. at what points does the graph intersect the y-axis?

We know that
the equation of a circle is
(x-h)²+(y-k)²=r²
where (h,K) is the center and
r is the radius

in this problem
the center is (0,0) and the radius is √81> r=9 units

the graph intersect the y-axis when x=0
so
x²+y²=81> 0+y²=81> y=(+/-)√81> y=(+/-) 9

the points are
(0,9)
and
(0,-9)

Subtracting is the opposite of adding