Q78 of 131 Page 226

In Fig. 9.32, area of ∆AFB is equal to the area of parallelogram ABCD. If altitude EF is 16 cm long, find the altitude of the parallelogram to the base AB of length 10 cm. What is the area of ∆DAO, where O is the mid point of DC?

We know that, area of a triangle = × b × h


and area of a parallelogram = b × h (corresponding height)


Given, Area of ∆AFB = Area of parallelogram ABCD


× AB × EF = DC × h


× 10 × 16 = 10 × h


10h = 80


h = 8 m


O is the mid point of DC, hence DO = × DC = × 10 = 5 m


Area of ∆DAO = × DO × h = × 5 × 8 = 20 m2


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