People's education printing plate sixth grade second volume mathematics classroom exercise book page 42 answer! Question: The area of the shaded part on the right is 40 square centimeters, and the area ratio of the big circle is smaller than that of the small circle. ... Explain this way: the area of the shadow part can be regarded as the area difference between two isosceles right triangles, that is, half the square of the radius of the big circle MINUS half the square of the radius of the small circle, (r? -r？ ) × 1/2, and how many square centimeters is the required area of a big circle larger than that of a small circle? You need to subtract the area of the small circle from the area of the big circle: 3. 14×R? -3. 14×r？ =3. 14×(R？ -r？ )

By (r? -r？ ) × 1/2=40 to get r? -r？ =80 The area of the great circle is larger than that of the small circle: 3.14× 80 = 251.2cm2.

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