Observer

The observer sees straight fence 100 m long in 30° view angle. From one end of the fence is 153 m.

How far is it from the another end of the fence?

Result

x =  179.9 m

Solution:

sinβsin30=15390 β=arcsin(15390sin30)=1.016=581242" γ=18030581242"=914718"  sinγsinβ=x153 x=153sinγsinβ=179.9  m \frac{ \sin \beta} { \sin 30^\circ } = \frac{ 153 } { 90 } \ \\ \beta = \arcsin ( \frac{ 153 } { 90 } \cdot \sin 30^\circ ) = 1.016 = 58^\circ 12'42" \ \\ \gamma = 180^\circ - 30^\circ - 58^\circ 12'42" = 91^\circ 47'18" \ \\ \ \\ \frac{ \sin \gamma} { \sin \beta } = \frac{ x } { 153 } \ \\ x = 153 \cdot \frac{ \sin \gamma} { \sin \beta } = 179.9 \ \text { m }

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