Given: A surveyor standing 50 feet from the base of a large tree measures the angle of elevation to the top of the tree as 75.8 degrees.
Required: To determine how accurately the angle must be measured if the percent error in estimating the tree's height is less than 5%.
Explanation: To estimate the angle, we will use the trigonometric ratio
[tex]tanx=\frac{h}{50}\text{ ...\lparen1\rparen}[/tex]where h is the tree's height, and x is the angle of elevation to the top of the tree.
Hence we get
[tex]\begin{gathered} h=50\cdot(tan75.8\degree) \\ h=197.59\text{ feet} \end{gathered}[/tex]Now differentiating equation 1, we get
[tex]sec^2xdx=\frac{1}{50}dh[/tex]We can write the above equation as:
[tex]sec^2x\cdot\frac{xdx}{x}=\frac{h}{50}\cdot\frac{dh}{h}\text{ ...\lparen2\rparen}[/tex]Also, it is given that the error in estimating the tree's height is less than 5%.
So
[tex]\frac{dh}{h}=0.05[/tex]Also, we need to convert the angle x in radians:
[tex]x=1.32296\text{ rad}[/tex]Putting these values in equation (2) gives:
[tex]\frac{dx}{x}=\frac{197.59}{50}\cdot\frac{cos^2(1.32296)}{1.32296}\cdot0.05[/tex]Solving the above equation gives:
[tex]\begin{gathered} \frac{dx}{x}=3.9518\cdot0.04548551012\cdot0.05 \\ =0.008987\text{ radians} \end{gathered}[/tex]Let
[tex]d\theta\text{ be the error in estimating the angle.}[/tex]Then,
[tex]\lvert{d\theta}\rvert\leq0.008987\text{ radians}[/tex]Final Answer:
[tex]\lvert{d\theta}\rvert\leq0.008987\text{ radians}[/tex]