[填空题]
A large plot of land is shaped like a tz lmas jy1z;,6rapezoid, ABCDy4 9ebesw 1t(;f+cb ms, where AB is parallel to CD, AB =12 km and CD =8 km. The diagonal B 1c+ts mb4(fw9;ybes eD of the trapezoid is equal to 10km. The internal angle $\mathrm{A}\hat{\mathrm{B}}\mathrm{D}$ is equal to 58$^{circ}$.
Let a new point, H, be a point on AB closest to D.
1.Calculate the distance from H to D. km
2.Calculate the length of AD. km
3.Calculate the size of the angle $\mathrm{D}\hat{\mathrm{A}}\mathrm{B}$. $^{circ}$
A landowner estimates that the length of AD is equal to 11.5 km.
4.Calculate the percentage error in the landowner's estimate. %
The landowner decides to install cone-shaped concrete bollards along the perimeter of the plot of land. The bollards are to be installed at a distance of 100 m from each other. The radius of the base of each bollard is 20 cm and the height of each bollard is 40 cm.
5.Calculate the volume of one of the bollards. $cm^3$
6.Calculate the total volume of concrete needed to install all the bollards. $cm^3$
