PERIMETER AND AREA 215

EXAMPLE 9 Find the area of the following triangles (Fig 11.20).

(i) Fig 11.20 (ii)
SOLUTION

(i) Area of triangle =

1

2 bh =

1

2 × QR × PS

=

1

2

×× 42 cm cm = 4 cm^2

(ii) Area of triangle =

1

2 bh =

1

2 × MN × LO

=

1

2

×× 32 cm cm= 3 cm^2

EXAMPLE 10 Find BC, if the area of the triangle ABC is 36 cm^2 and the height AD is
3 cm (Fig 11.21).

SOLUTION Height = 3 cm, Area = 36 cm^2

Area of the triangle ABC =

1

2

bh

or 36 =

1

2

××b (^3) i.e., b = 36 2
3
×
= 24 cm
So, BC = 24 cm
EXAMPLE 11 In ΔPQR, PR = 8 cm, QR = 4 cm and PL = 5 cm (Fig 11.22). Find:
(i) the area of the ΔPQR (ii) Q M
SOLUTION
(i) QR = base = 4 cm, PL = height = 5 cm
Area of the triangle PQR =
1
2
bh

1
2
×× 45 cm cm = 10 cm^2
Fig 11.21
Fig 11.22
S