Ex 11.2, 8 ΔABC is isosceles with AB = AC = 7.5 cm and BC = 9 cm (Fig 11.26). The height AD from A to BC, is 6 cm. Find the area of Δ ABC. What will be the height from C to AB i.e., CE?
Finding area of ∆ABC
Using BC as base and
AD as height
Here,
Base = BC
= 9 cm
Height = AD
= 6 cm
Area of ∆ABC = 1/2 × Base × Height
= 1/2 × BC × AD
= 1/2 × 9 × 6
= 9 × 3
= 27 cm2
Now, we have to find EC which is height corresponding to base AB
So, finding Area using EC as height and AB as base
Base = AB = 7.5 cm
Height = EC = ?
Area of ∆ABC = 1/2 × Base × Height
27 = 1/2 × 7.5 × EC
(27 × 2)/7.5 = EC
(27 × 2 × 10)/75 = EC
(9 × 2 × 10)/25 = EC
(9 × 2 × 2)/5 = EC
36/5 = EC
7.2 = EC
EC = 7.2 cm
∴ Area of ∆ABC is 27 cm2
and Height CE is 7.2 cm

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 13 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.

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