Circle with Centre (0,0) (Leaving Cert Mathematics): Flashcards

A circle positioned at the origin

(0,0), where x-axis and y-axis meet

Distance from centre to any point on circle

Set of points same distance (radius) from centre

$x^2 + y^2 = r^2$

$x^2 + y^2 = 9$

Substitute $r$ into $x^2 + y^2 = r^2$

Use distance formula to find $r$ first

$r = sqrt{x^2 + y^2}$

Take square root of the constant

Rearrange first before identifying radius

$r = sqrt{8} = 2sqrt{2}$

Divide by 9 to get x^2 + y^2 = rac{16}{9}