SOLUTION: DIFF CALCULUS:an airplane is flying horizontally at an altitude of 9000m. an observer on the ground notice that when the angle of elevation of the plane is 60 degrees, the angle de

We want to find dx/dt when θ = 60°,

So we list what we need to substitute when θ = 60°,
so we can solve for dx/dt:

 

dθ/dt = -0.15 (negative because θ is decreasing as
the plane moves to the right.)

       , so , and
 


Substituting,



Multiply both sides by -3000





Edwin