面积如果将一个平面图形,不变它的原来形状,把它放大(或缩小),如用照像放大,或放大尺放大等,图形的面积是和图形上的任何一个相当尺寸的平方成正比例。例1.例如四个正方形,它们的边长是1公分(cm),2公分,3公分,和4公分,那末它们的面积各是1平方公分,4平方公分,9平方公分,16平方公分(如图)。因为正方形面积=边长×边长; 1公分×1公分=1平方公分, If the area is a planar image, its original shape is not changed, and it is enlarged (or reduced), such as zooming in with a photo, or zooming in on a scale, and the area of ​​the figure is proportional to the square of any comparable size on the figure. . Example 1. For example, the four squares, whose side lengths are 1 cm (cm), 2 cm (3 cm), 4 cm (4 cm), and their area are 1 cm 2 , 4 cm 2 , 9 cm 2 , 16 cm 2 (Figure). Because square area = length of side × length of side; 1cm × 1cm = 1cm2,