let us suppose a side of the square = s

then, the area of the square would be s^2

Diagonal BE of the square is the hypotenuse of the triangle BAC

Since the triangle is a 45-45-90 triangle the hypotenuse must measure s√2

For the parallelogram notice that the area of the parallelogram = area of triangle BCE and area of triangle CED

Side BE//CD and CE is the transversal so triangle BCE and triangle CED are similar

<BCE=<CED=90degree

<BEC=<ECD

Since the two triangle share the same side the triangles have equal length of sides. This follows

area of parallelogram = 2* area of triangle BCE

area of triangle BCE= 1/2*s*s=s^2/2

area of parallelogram = s^2/2*2= s^2

area of square = area of parallelogram

(c)

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This is my response to the question and may be incorrect. Feel free to rectify any mistakes