#13 p256: A plane, 7 miles in the air flies over a radar antenna.
#13 p256: The moment that the plane is 10 miles from the radar,
#13 p256: the distance from the radar to the plane is changing
#13 p256: at a rate of 300 mi/hr. How fast is the plane flying horizontally?
var('z,zp,xp')
show(z^2==x^2+49)
show(2*z*zp==2*x*xp)
show(2*10*300==2*sqrt(51)*xp)
show(solve(2*10*300==2*sqrt(51)*xp,xp)[0].rhs().n())
#xp is about 420.084 mi/hr