Question

a circle has its centre at the origin and has the rquation x^2+y^2=81 what is the size of the radius​

Answer 1

radius = 9

Explanation:

the equation of a radius centred at the origin is

x² + y² = r² ( where r is the radius )

x² + y² = 81 ← is in standard form

with r² = 81 ( take square root of both sides )

r =
`√(81)` = 9