NCERT Figure it Out 1 - Q4 - Quadrilaterals
Question: We have seen how to get 90 deg using paper folding. Now, suppose we do not have any paper but two sticks of equal length, and a thread. How do we make an exact 90 deg using these?
Answer: Cross equal sticks at their midpoints; the quadrilateral of endpoints is a rectangle, so each corner is 90 deg.
Full step-by-step NCERT solution with diagrams on Something by Zero.