Thus the (four) outer
half-rectangles of width 3, length 4, and diagonal 5,
together make two rectangles (of area 24); then (when
this is subtracted from the square plate of area 49) the
remainder is of area 25.
This (process) is called 'piling
up the rectangles' (chi chu).
From the Chou pai suan ching, quoted in Swetz and Kao, 1877.