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Suppose a person is standing on the top of a building and that she has an instrument that allows her to
measure angles of depression. There are two points that are 100 feet apart and lie on a straight line that is
perpendicular to the base of the building. Now suppose that she measures the angle of depression from the
top of the building to the closest point to be 33.5º and the angle of depression from the top of the
building to the furthest point to be 28.3º. Determine the height of the building. (Round your answer to the
nearest tenth of a foot.)

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MrRoyal MrRoyal · Answer 1 · 2022-04-26T15:15:25+02:00

The building and the person on it are illustrations of elevation and depression

The height of the building is 76.9 feet

To calculate the building height, we make use of the attached illustration

Considering the triangle DCB in the figure, we have:

tan(B) = DC/BD

Substitute known values

tan(28.3) = DC/(DA + 100)

Cross multiply

(DA + 100) * tan(28.3) = DC

Divide both sides by tan(28.3)

DA + 100 = DC/tan(28.3)

Subtract 100 from both sides

DA = -100 + DC/tan(28.3)

Considering the triangle DCA in the figure, we have:

tan(A) = DC/DA

Substitute known values

tan(33.5) = DC/DA

Make DA the subject

DA = DC/tan(33.5)

Substitute DA = DC/tan(33.5) in DA = -100 + DC/tan(28.3)

DC/tan(33.5) = -100 + DC/tan(28.3)

Evaluate the tangent ratios

0.56DC = -100 + 1.86DC

Collect like terms

-1.86DC + 0.56DC = -100

Evaluate

-1.3DC = -100

Divide both sides by -1.3

DC = 76.9 feet

Hence, the height of the building is 76.9 feet

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