NCERT Visualise - Cut square corners - Exploring Some Geometric Themes
Question: Cut off the four corners of an imaginary square, with each cut going between midpoints of adjacent edges. What shape is left? How can you reassemble the four corners to make another square?
Answer: A regular octagon remains. The four corner triangles reassemble into a smaller square (pair hypotenuses / match equal legs).
Full step-by-step NCERT solution with diagrams on Something by Zero.