[填空题]
A large plot of land is shap51ioz)pjq )4nxjml onv *f0-o ed like a ez.ny;2kj (b aleh5z; l0v3kq trapezoid, ABCD, where AB is parallel to CD, AB = 12 km and CD =8 km. The diaykk(3njb vq;.a ;5e lh20zze lgonal BD of the trapezoid is equal to 10 km. 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. $cm^3$
