Let AB=L 1, CD=L2, BD=L3, then:

Elevation angle β = Actan [(L2-L1)/L3] = Actan [(75-50)/120] =1/46' 5.84 "

Depression angle α = Actan (l1/L3) = Actan (50/120) = 22 37'11.

2. Solution: (The picture is above, assuming AB is a person and CD is a flagpole)

As shown, then:

β=40，BD=L3= 12m

The human eye is off the ground l1=1.5m.

Then:

Flagpole height L3 = l 1+tanβ* L3

That is L3 = 1.5+tan 40 * 12.

= 2.33 meters