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Trigonometry / Sine rule

To calculate the length of a submarine, Mervyn
stands on a cliff 60 m high and measures the angle
of depression of both ends of the boat.
The information is shown in the diagram.

a Find the value of the angle DAB.
b Use trigonometry to calculate the length AB.
c Use the sine rule to work out the length BC.
Original post by zzzxl
To calculate the length of a submarine, Mervyn
stands on a cliff 60 m high and measures the angle
of depression of both ends of the boat.
The information is shown in the diagram.

a Find the value of the angle DAB.
b Use trigonometry to calculate the length AB.
c Use the sine rule to work out the length BC.


http://www.thestudentroom.co.uk/showthread.php?t=2913007
Reply 2
Avatar for zzzxl
zzzxl
OP
Original post by the bear


Sorry, new here but how do I see the answer there? :smile:
Original post by zzzxl
Sorry, new here but how do I see the answer there? :smile:


oops... i thought someone had answered it...

anyway to find angle DAB you subtract another angle from 90°

then you look at the 90° triangle on the left. the height of the cliff is the adjacent to angle DAB. you are trying to find the hypotenuse....

once you have found the hypotenuse move on to the obtuse angled triangle and apply what you know using the sine rule to answer the final part.

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