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Mathematics

Two similar triangles ABC and DEF such that area of Δ ABC = 64 sq. unit and area of Δ DEF = 121 sq. unit.

Statement (1) : Perimeter of Δ DEFPerimeter of Δ ABC=811\dfrac{\text{Perimeter of Δ DEF}}{\text{Perimeter of Δ ABC}} = \dfrac{8}{11}.

Statement (2) : The ratio of perimeters of two similar triangles is equal to the ratio of their areas.

  1. Both the statement are true.

  2. Both the statement are false.

  3. Statement 1 is true, and statement 2 is false.

  4. Statement 1 is false, and statement 2 is true.

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Answer

Given, △ ABC ∼ △ DEF.

We know that,

The ratio of the areas of two similar triangles is equal to the square of the ratio of their corresponding sides.

Area of Δ DEFArea of Δ ABC=DE2AB212164=DE2AB2AB2DE2=64121ABDE=64121ABDE=811\therefore \dfrac{\text{Area of Δ DEF}}{\text{Area of Δ ABC}} = \dfrac{DE^2}{AB^2}\\[1em] \Rightarrow\dfrac{121}{64} = \dfrac{DE^2} {AB^2}\\[1em] \Rightarrow \dfrac{AB^2}{DE^2} = \dfrac{64}{121} \\[1em] \Rightarrow \dfrac{AB}{DE} = \sqrt{\dfrac{64}{121}}\\[1em] \Rightarrow \dfrac{AB}{DE} = \dfrac{8}{11}

Since, corresponding sides of similar triangle are proportional.

ABDE=BCEF=ACDF\Rightarrow \dfrac{AB}{DE} = \dfrac{BC}{EF} = \dfrac{AC}{DF}

We know that,

For any two or more equal ratios, each ratio is equal to the ratio between sum of their antecedents and sum of their consequents.

ABDE=AB+BC+ACDE+EF+DFPerimeter of Δ ABCPerimeter of Δ DEF=ABDEPerimeter of Δ DEFPerimeter of Δ ABC=DEAB=118\Rightarrow \dfrac{AB}{DE} = \dfrac{AB + BC + AC}{DE + EF + DF} \\[1em] \Rightarrow \dfrac{\text{Perimeter of Δ ABC}}{\text{Perimeter of Δ DEF}} = \dfrac{AB}{DE} \\[1em] \Rightarrow \dfrac{\text{Perimeter of Δ DEF}}{\text{Perimeter of Δ ABC}} = \dfrac{DE}{AB} = \dfrac{11}{8}\\[1em]

So, statement 1 is false.

The ratio of perimeters of two similar triangles is equal to the ratio of their corresponding sides.

So, statement 2 is false.

Hence, option 2 is the correct option.

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