Q53 / 90 · JEE Main 2021 (25 Jul Shift 2) · Mathematics

If a rectangle is inscribed in an equilateral triangle of side length 22 as shown in the figure, then the square of the largest area of such a rectangle is _____.

Figure

Correct answer: 3

Solution

Figure

In ΔDBF,

tan60°=2b22-ℓ

⇒b=322-ℓ2

A=Area of rectangle

=ℓ×b

⇒A=ℓ×3222-ℓ

On differentiating, we get

dAdℓ=3222-ℓ-ℓ·32=0

⇒ℓ=2

Now, A=ℓ×b

=2×322=3

⇒A2=3.

Hence, the correct answer is 3.

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