Rectangular Coordinate System (I) 8.45
rotation ૅᔷ gear ቃ
(b) Distance between Q(-3 , -5) and l2
= [1 - (-3)] units
= 4 units
Diagram Clue
M(1,-2)
y
x
m2
O
Q(-3,-5)
R
4 units
4 units
` Coordinates of R = (-3 + 2 # 4 , -5)
= (, )55The x-coordinate
of
any point on the vertical line
l2 is 1.
◀ reflected to the right
◀
C Rotation
In the figure, the centre of the gear and a point on the edge are denoted
by O and P respectively. The gear is rotated clockwise about O through
90c:
O
P
O
90°
P'
clockwise
direction
P is also rotated clockwise about O through 90c to Pl. This kind of
transformation is called rotation of a point and the fixed point O is called
the centre of rotation.
In the figure, l1 is a line parallel to the
x-axis and l2 is a line parallel to the y-axis.
B is the image when a point A(3 , -2) is
reflected in l1.
(a) Find the coordinates of B.
(b) If C is the image when B is reflected
in l2, find the coordinates of C.
16
Instant Drill
➥ Ex 8D 20
A(3 ,- 2)
D(1,1)
y
x
m2
m1
O
(3 , 4) (-1 , 4)