| The three silk fans are completely unfolded just to form a circle, ∴ the radius of the large circle can be obtained as 30cm (1 point); It can be seen that the radius of the small circle is 12cm. ∴ S large circle = πr 2 =30 2 π=900π (2 points); S small circle = πr 2 =122 π=900π (2 points); S small circle = πr 2 =122 π=900π (2 points). Small circle = πr 2 =12 2 π=144π.(3 points) ∴S silk surface =S large circle -S small circle =900π-144π=756π.(4 points) ∴The area of silk cloth required for the two silk fans is:
| ||
| 2 | ||
| 3 |