[填空题]
The following diagra8jl:0 xmr e(lum pus.2y 1h:eyg8s4 -cubp0 ug.vllh,e6 j uk(hshows a circular crop field.
The circle has centre O and a radius of 400 $\mathrm{~m}$ , and the points $\mathrm{A}$, $\mathrm{B}$, $\mathrm{C}$ and $\mathrm{D}$ lie on the circle. The angle $\mathrm{AOB}$ is 1.6 radians.
1. Find the length of chord A B .≈
2. Find the area of triangle A O B .
The angle BOC is 2.5 radians.≈
3. Find the length of the minor arc AC.≈
4. Find the area of the shaded region.
The shaded region is to be planted with corn. Corn seeds are sold in bags which cost 140 dollars each. One bag is enough for seeding 8960 $\mathrm{~m}^{2}$ .≈
5. Find the cost of the corn seeds.
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