1. The cover area of a math book is about 40 square centimeters, which is consistent with the actual situation. 4 square decimeters =400 square centimeters, and 400 square centimeters is 15 centimeters long times about 26.6 centimeters wide, which is the size of a book.

2, 4 square centimeters, this area is too small, a book can not be as big as 4 square centimeters, 4 square centimeters is 2 centimeters long and 2 centimeters wide. The length and width of this book are all over 2 cm.

3,400 square centimeters, which is too big.

Extended data

First, the area conversion source:

In the 7th century AD, Brahmagupta developed a formula, which is now called Brahmagupta formula, to calculate the area of a circular quadrilateral on its side (the quadrilateral is carved in a circle). ?

1842, German mathematicians Karl Anton Bretschneider and Karl Georg Christian von Staudt independently discovered a formula called Bretschneider formula, which can be applied to any quadrilateral area.

Second, the unit conversion:

1 cm2 = 1 00mm2, 1 mm2 = 1 00mm2,1m2 =1cm2,1m2 =/kloc-0. 1 ha = 1 0000m2, 1 km2 = 1 00000m2 =100000m2,1km2 =100000m2 =

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