Question 76650
While the plane is gliding it goes from C to A. AB is ground and BC is the altitude.


{{{drawing(400,400,-350,50,-50,350,
line(0,0,-285,0),
line(-285,320,-285,0),
arrow(-285,320,0,0),
locate(-90,150,17000),
locate(-200,-5,15000),
locate(0,-2,A),
locate(-285,-2,B),
locate(-275,335,C)
)}}}


Apply Pythagorus theorem.
{{{AC^2 = AB^2 + BC^2}}}
or {{{17000^2 = 15000^2 + BC^2}}}
or {{{BC^2 = 17000^2 - 15000^2}}}
or {{{BC^2 = 64000000}}}
or {{{BC = sqrt(64000000)}}}
or {{{BC = 8000}}}


So, the altitude of the plane from its starting point is 8000 ft.