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:
Other area calculation:
Rectangle: {rectangular area = length × width}
Square: {Square area = side length × side length}
Parallelogram: {parallelogram area = base × height}
Triangle: {Triangle area = base × height ÷ 2}
Trapezoid: {Trapezoid area = (upper bottom+lower bottom) × height ÷ 2}
Circle (perfect circle): {area of circle (perfect circle) = π× radius× radius}
Circular ring: {circular (outer ring) area = {pi × (outer ring radius 2- inner ring radius 2)