ABCD is a square such that [ABCD] = 120. E, F, G, H are the midpoints of AB, BC, CD and DA respectively. What is [EFGH]?
Details and assumptions:
[PQRS] denotes the area of figure PQRS.
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Step-by-step explanation:
AE = BF = CG = DH = x (say)
BE = CF = DG = AH = y (say)
In ΔAEH and ΔBEF, we have
AE = BF
∠A = ∠B
And
AH = BE
So, by SAS congruency criterion,
we have
ΔAEH ≃ ΔBFE
∠1 = ∠2 and
∠3 = ∠4
But ∠1 + ∠3 = 90°
and ∠2 + ∠A = 90°
∠1 + ∠3 + ∠2 + ∠A = 90° + 90°
∠1 + ∠4 + ∠1 + ∠4 = 180°
2(∠1 + ∠4) = 180°
∠1 + ∠4 = 90°
HEF = 90°
Similarly we have ∠F = ∠G = ∠H = 90°
Hence, EFGH is a Square.
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