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The answer to the question on page 34 of the first volume of the sixth grade mathematics classroom exercise book of Zhejiang Education Press! Ask good people for help!
The left side is actually the fan area:

π×8^2 ÷2-π×5^2÷2

=π×(64-25)÷2

=3. 14×39÷2

=6 1.23(dm^2)

That is, (π times the square of 8 divided by 2-π times the square of 5 divided by 2)

On the right is the area of the square-the area of the circle:

4^2-π×(4÷2)^2

= 16-4π

3.44(cm^2)

Key point: the area formula of the circle: π r 2.

Sector area formula: π r 2-π r 2.