Q29 of 49 Page 1

From a point P on the ground, the angle of elevation of the top of a 10 m tall building is 30o. A flagstaff is fixed at the top of the building and the angle of elevation of the top of the flagstaff from P is 45o. Find the length of the flagstaff and the distance of the building from the point P? [Take √3 = 1.73]

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Let QR = 10 m be the building and RS be the flagstaff.


In Δ PQR,


tan 30° = QR/PQ


1/√3 = 10/PQ


PQ = 10√3 m = 10× 1.73 = 17.3 m


In Δ PQS,


tan 45° = QS/PQ


1 = QS/17.3


QS = 17.3 m


Thus, Length of the flagstaff = RS = QS-QR = 17.3 – 10 = 7.3 m


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