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Question

A square and an equilateral triangle have equal perimeters. If the diagonal of the square is 122 cm, then the area of the triangle is:

A
242 cm2
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B
243 cm2
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C
483 cm2
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D
643 cm2
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Solution

The correct option is D 643 cm2
Let ABCD be a square.
Given, diagonal of the square 122 cm.
Then, BD = 122 cm


BCD=90 ( ABCD is a square)
Then, by Pythagoras' theorem, we have
2(DC)2=(122)2
DC2=144×22DC=12 cm

Perimeter of square=4(12)=48 cm
(AB=BC=CD=AD)

Given, the square and equilateral triangle have equal perimeters.
Perimeter of an equilateral triangle with side 'a' is 3a.
So, 3a=48
a=483=16 cm

We know, area of an equilateral triangle with side 'a' is given by 34a2.

Area=34(16)2 =34×16×16 =643 cm2


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