fpprintprec:5;

with_slider_draw(
       a, makelist(i, i, 0, 150),
       color=blue,
       line_width=3,
       head_length=50,
       vector([0,0],[0,800]),
       xrange=[-500,500],
       yrange=[-150,850],
       proportional_axes=xy,
       color=red,
       vector([0,0],[a/sqrt(2),-a/sqrt(2)]),
       color=brown,
       vector([0,0],[a/sqrt(2),800-a/sqrt(2)]),
       color=red,
       label([concat("wind speed = ",string(a)),250,100]),
       color=blue,
       label([concat("plane speed = ",string(800)),-250,400]),
       color=brown,
       label([concat("ground speed = ",string(float(sqrt((a/sqrt(2))^2+(800-a/sqrt(2))^2)))),250,400]),
       pic_width=700,
       pic_height=500)$

fpprintprec:0;

float(sqrt((50/sqrt(2))^2+(800-50/sqrt(2))^2));