Answer:
see explanation
Step-by-step explanation:
the equation of a circle centred at the origin is
x² + y² = r² ( r is the radius )
(11)
- 81 + x² = - y² ( add y² to both sides )
- 81 + x² + y² = 0 ( add 81 to both sides )
x² + y² = 81 ← in standard form
with centre = (0, 0 ) and r = [tex]\sqrt{81}[/tex] = 9
(12)
y² + x² - 196 = 0 ( add 196 to both sides )
x² + y² = 196 ← in standard form
with centre = (0, 0 ) and r = [tex]\sqrt{196}[/tex] = 14
