1. r > 0 Does circles touch externally or internally ? radius = (a,b)
centre = (-g,-f)
(x - a)2 + (y - b)2 = r2
x2 + y2 + 2gx + 2fy + c =0
Finding centre and radius
from circle equation
Equation
from graph
Is equation
a circle ?
r > 0
Circle TYPE questions
(Straight Line , Quadratics)
Intersection
points between
line and circle
(a,b)
Equation
of tangent
Steps
Sub line equation y = ...
into circle.
Discriminant to establish
how many points.
Factorise for x coordinates
and sub into line equation
for y coordinates
3 possible
scenarios
Steps
Find gradient of
centre to point
Use m1 x m2 = -1
to find gradient of line
Use y – b = m(x - a)