GROUP 1: CENTRE
Key words: centre, radius, diameter
AB= BC
(line from centre L chord)
B =B, =90°
(line from centre to mpt chord)
=2A
(
at centre = 2x2 at circ)
A =90°
(
in semi O)
GROUP 2: CYCLIC QUADRILATERALS
Key words: cyclic quadrilateral, concyclic (cyclic quads are often not mentioned in the wording
ofa question - LOOK FOR four points on the circumference of a circle:
A+B=180° and +D=180°
(opp Zs of cycl quad)
Q
(ext
.
of cycl quad)
A=B and C=D
(Zs in same segment)
GROUP 3: TANGENTS
Key words: tangent, touch
B
= B, =90
(rad L tan)
PQ=PR
(tangents from same pt)
(tan chord thm)
A
233
or)
OA OB
DON'T FORGET:
(radii)
A B
(equal chords > equal s )
STILL MISsSING SOMETHING?
Remember what you've learnt in Grades 8 and 9:
(corresp 2s; AB || CD)
Parallel lines
C
-D
(alt 2s; AB||CD)
P2+Q=180° (co-int Zs;AB||CD)
A+B+C =180° (Zs of )
Triangles
Points
=A+B
(ext 2
B-C
(Zs opp= sides)
AB= AC
(sides opp= Zs)
of A)
O, -0, and ô,=ô,
0,+0,=180
(vert opp 2s)
(Zs on a str In)
o, +O +Ô, = 360°
(s round a pt)
FURTHER TIPS
Angle at the circumference: Follow the arms of the angle to the circumference. From the two
points at the circumference, follow two other lines to the:
.
circumference (in the same segment)
Zs in same segment
2.
circumference (in the opposite segment)
opp Zs of cycl quad
+X=180°
centre
A
L at centre = 2x2 at cire
234