Explain how you know the origin is the centre of the circle defined by the equation x2+y2=45.

X² + y² = 45
x² - x² + y² = 45 - x²
y² = 45 - x²
y = 3√(5) - x
x² + (3√(5) - x)² = 45
x² + 45 - x² = 45
x² - x² + 45 = 45
0x² + 45 = 45
        -45  -45
        0x² = 0
         0      0
         x² = 0
          x = 0
(0)² + y² = 45
   0 + y² = 45
  -0            -0
        y² = 45
         y = 3√5
(x y) = (0, 3√5)