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Mathematics

ΔABC and ΔDEF are similar to each other. If the ratio of side AB to side DE is (2+1):3(\sqrt{2} + 1) : \sqrt{3}, then the ratio of area of ΔABC to that of ΔDEF is:

  1. (3+22):3(3 + 2\sqrt{2}) : 3

  2. 1:(962)1 : (9 - 6\sqrt{2})

  3. (962):2(9 - 6\sqrt{2}) : 2

  4. (322):3(3 - 2\sqrt{2}) : 3

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Answer

Given,

ΔABC and ΔDEF are similar to each other.

Since the triangles are similar, the ratios of Areas of triangles is equal to squares of corresponding sides.

Area of triangle ABCArea of triangle DEF=((2+1)3)2=(2+1)2(3)2=(2)2+(1)2+2×2×13=2+1+223=3+223.\Rightarrow \dfrac{\text{Area of triangle ABC}}{\text{Area of triangle DEF}} = \Big(\dfrac{(\sqrt{2} + 1)}{\sqrt{3}}\Big)^2 \\[1em] = \dfrac{(\sqrt{2} + 1)^2}{(\sqrt{3})^2} \\[1em] = \dfrac{(\sqrt{2})^2 + (1)^2 + 2 \times \sqrt{2} \times 1}{3} \\[1em] = \dfrac{2 + 1 + 2\sqrt{2}}{3} \\[1em] = \dfrac{3 + 2\sqrt{2}}{3}.

Area of triangle ABC : Area of triangle DEF = (3+22):3(3 + 2\sqrt{2}) : 3.

Hence, option 1 is the correct option.

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