Page 142 - Math Smart - 7
P. 142
Investigate
AC and BD are straight lines that
Intersect at point O.
Prove that vertically opposite angles
are equal at a point.
O Calculate angle a.
Q Calculate angle b.
Q Calculate angle c.
Q What do you notice about the size of angles a and c?
0 What do you notice about the size of angles DOC and AOBl
Conclusion:
Vertically opposite angles are .
There are pairs of vertically opposite angles at a point.
Example 4
in the diagram, AB and CD are straight lines.
Verticaily opposite angles
are equal. If -40D = 137°, calculate the size of:
O COS, 0 /IOC and Q BOD.
Solution
0 c6B = AdD (vert. opp. zls)
Remember to state the reason
= 137° 'vert. opp. ^s'.
0 A6D + A6C=^80° s on str. line)
/^6C= 180°-137°
= 43°
0 BOD = AOC (vert. opp. /Ls)
= 43°
UNIT 6 Angles and Their Properties
