As the picture shows, the hydrogen balloon with the banner of "Celebrating the Third Anniversary of Haimen Experimental School" rises over the campus. It is known that the diameter of the balloon is 4m, which is measured at point A on the ground. Solution: Connect oc.

∫ The diameter of the balloon is 4m, the radius is 2m, and the measured viewing angle of the balloon is ∠ BAC = 2 (AB and AC are tangents of ⊙O, and B and C are tangents).

∴∠OAC= 1，

In Rt△OAC, OC=2m, ∠ OAC = 1,

∫sin 1 = OCAO，

∴ao=20.0 175= 1 14.2(m).

In Rt△OAD, there is OD = OA× SIN 60 ≈ 99 (m).

A: The height OD of the balloon center from the ground is about 99 meters. ..