Or
The angle of elevation of an aeroplane from a point on the ground is 60°. After a flight of 15 seconds, the angle of elevation changes to 30°. If the aeroplane is flying at a constant height of 1500
m, find the speed of the aeroplane.
Ans. 200 m/s or 720 km/hr
See Q. 27, 2002 (III Delhi).
Q. 28. Prove that in a right triangle, the square on the hypotenuse is equal to the sum of the squares on the other two sides.Making use of the above, prove the following :In a rhombus ABCD, prove that
4 AB2 = AC2 + BD2.
Sol. Part I. See Theorem 3, Page (xxxi).
Part II.
Given. In rhombus ABCD,
diagonals AC and BD intersect
at O
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