Standing on one bank of a river, an explorer measures the angle to the top of a tree on the opposite bank to be 27 degrees. He backs up 50 feet and measures the angle to the top of the tree to now be 22 degrees. How wide is the river? Round to the nearest tenth of a foot.

Respuesta :

Answer: 191.5 feet

Step-by-step explanation:

You can observe two right triangles in the figure attached: ABC and DBC.

Where the width of the river is "x".

Remember the trigonometric identity:

[tex]tan\alpha=\frac{opposite}{adjacent}[/tex]

Then, for the triangle ABC:

[tex]tan(22\°)=\frac{CB}{AB}\\\\tan(22\°)=\frac{CB}{50+x}[/tex]

Solve for CB:

[tex](50+x)*tan(22\°)=CB[/tex]     [Equation 1]

For the triangle DBC:

[tex]tan(27\°)=\frac{CB}{DB}\\\\tan(27\°)=\frac{CB}{x}[/tex]

Solve for CB:

[tex]xtan(27\°)=CB[/tex]              [Equation 2]

Making [Equation 1]=[Equation 2] and solving for "x", you get:

[tex](50+x)*tan(22\°)=xtan(27\°)\\\\50tan(22\°)+xtan(22\°)=xtan(27\°)\\\\50tan(22\°)=xtan(27\°)-xtan(22\°)\\\\50tan(22\°)=(tan(27\°)-tan(22\°))x\\\\x=\frac{50tan(22\°)}{tan(27\°)-tan(22\°)}\\\\x=191.5ft[/tex]

Ver imagen luisejr77

The width of the river can be found using trigonometric ratios. Therefore, the width of the river is 191.5 ft

The situation forms a right angle triangle

What is a right angle triangle?

A right angle triangle has one of its angles as 90 degrees. The sides and angles can be found using trigonometric ratios.

Therefore, the opposite side is the height of the tree. The width of the river can be found using trigonometric ratios:

tan ∅ = opposite / adjacent

tan 27° = h / x

tan 22° = h / x + 50

where

x = width of the river

h = height of tree

Therefore,

x tan 27° = h

x + 50 tan 22° = h

Hence,

x tan 27° = (x + 50) tan 22°

x tan 27° = x tan 22° + 50 tan 22°

x tan 27° - x tan 22° = 50 tan 22°

x(0.10549922365) = 20.2013112918

x = 20.2013112918 / 0.10549922365

x = 191.483032698

x = 191.5 ft

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