# Help with angles?

• Nov 13th 2012, 11:22 AM
jackles88
Help with angles?
A river runs parallel to a block of flats. The roof of this block is 20m above the water level of the river. From a point R on the roof, looking directly across the river, the angle of depression of the nearer bank N is 43 degrees and the angle of depression of the farther bank F is 23 degrees. The bottom of the block of flats may be regarded as a point B.

a) Draw a diagram to display this information, showing clearly the points R, B, F and N and the angles of depression.

b)Calculate the width of the river, FN, correct to 3 significant figures

c) Calculate the distance from the roof to the near side of the river, RN, correct to the nearest whole number.

Im really stuck with how i draw the diagram? And then the method of how to work out the other questions.(Worried) If anyone can help it'd be much appreciated.

• Nov 13th 2012, 12:56 PM
skeeter
Re: Help with angles?
sketch ...
• Nov 18th 2012, 11:45 AM
alirizagurcali
Re: Help with angles?
could you please post the method of working out the other questions b and c
thank you
• Nov 18th 2012, 12:06 PM
skeeter
Re: Help with angles?
let $\displaystyle |BN| = x$ , $\displaystyle |NF| = w$

$\displaystyle \tan(43^\circ) = \frac{20}{x}$

$\displaystyle \tan(23^\circ) = \frac{20}{x+w}$

solve the system for $\displaystyle x$ and $\displaystyle w$ , then you can answer (c) using Pythagoras.