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If Abcd is a Parallelogram, Then Prove that ๐‘Ž๐‘Ÿ (ฮด๐ด๐ต๐ท) = ๐‘Ž๐‘Ÿ (ฮด๐ต๐ถ๐ท) = ๐‘Ž๐‘Ÿ (ฮด๐ด๐ต๐ถ) = ๐‘Ž๐‘Ÿ (ฮด๐ด๐ถ๐ท) = `1/2` ๐‘Ž๐‘Ÿ (||๐‘”๐‘š ๐ด๐ต๐ถ๐ท) .

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Question

If ABCD is a parallelogram, then prove that
๐‘Ž๐‘Ÿ (Δ๐ด๐ต๐ท) = ๐‘Ž๐‘Ÿ (Δ๐ต๐ถ๐ท) = ๐‘Ž๐‘Ÿ (Δ๐ด๐ต๐ถ) = ๐‘Ž๐‘Ÿ (Δ๐ด๐ถ๐ท) = `1/2` ๐‘Ž๐‘Ÿ (||๐‘”๐‘š ๐ด๐ต๐ถ๐ท) .

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Solution

Given: ABCDis a parallelogram
To prove : area  (Δ๐ด๐ต๐ท) = ๐‘Ž๐‘Ÿ (ΔA๐ต๐ถ) = are  (Δ ACD)

 = `1/2` ๐‘Ž๐‘Ÿ (||๐‘”๐‘š ๐ด๐ต๐ถ๐ท)

Proof: we know that diagonals of a parallelogram divides it into two equilaterals.
Since, AC is the diagonal.

Then, ๐‘Ž๐‘Ÿ (Δ๐ด๐ต๐ถ) =   (Δ ACD) = `1/2` ๐‘Ž๐‘Ÿ (||๐‘”๐‘š ๐ด๐ต๐ถ๐ท)............ (1)

Since, BD is the diagonal

Then, ๐‘Ž๐‘Ÿ (Δ๐ด๐ต๐ถ) = ๐‘Ž๐‘Ÿ (Δ๐ต๐ถ๐ท)  = `1/2` ๐‘Ž๐‘Ÿ (||๐‘”๐‘š ๐ด๐ต๐ถ๐ท)............ (2)

Compare equation (1) and (2)

∴ ๐‘Ž๐‘Ÿ (Δ๐ด๐ต๐ถ) =  ๐‘Ž๐‘Ÿ (Δ๐ด๐ถ๐ท)

 = ๐‘Ž๐‘Ÿ (Δ๐ด๐ต๐ท) =  ๐‘Ž๐‘Ÿ (Δ๐ต๐ถ๐ท) =   `1/2` ๐‘Ž๐‘Ÿ (||๐‘”๐‘š ๐ด๐ต๐ถ๐ท)

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Chapter 14: Areas of Parallelograms and Triangles - Exercise 14.2 [Page 15]

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R.D. Sharma Mathematics [English] Class 9
Chapter 14 Areas of Parallelograms and Triangles
Exercise 14.2 | Q 4 | Page 15

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