telescope is 310ft above ground and bike is approaching at 10ft/sec whatrate is...

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Yoyoyo

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...the angle changin when 100 awa A man standing on a building is watching a bicycle through a telescope as it approaches the building directly below. If the telescope is 310 ft about ground level and if the bicycle is approaching the building at 10 ft/sec, at what rate is the angle changing when the bicycle changing when the bicycle is 100 ft from the building. And the angle it is referring to is the one on the outside of the triangle not the one inside.
 
let x be horizontal distance
let y be the angle of elevation
5any=310/x
y=arctan310/x
dy/dt=(1/(1+(310/x)^2)))(-1/x^2)dx/dt
dx/dt=-10
x=100 substitute and solve for dy/dt
 
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