A math problem on the green grassland, the wolf thinks about how to catch sheep every day, and always fails and tries, never giving up. As the picture shows, one day, the wolf was there.
According to the meaning of the question, the angle BAD = 60°∠CBD = 30°,
In Rt△BCD, let CD=x, then BD = X 3 root sign.
In Rt△ABD, ∠ bad = 60,
AD=BD times tan60 =3x.
So x+40=3x.
The solution is x=20.
So BD= root number 3×20=35.
Time t=35 divided by 5=7 seconds.