[填空题]
A ladder that is 6 m lo 6n 9k/5a :pdwnu1ryoo wj d7axrh.y4)hv0ewl1 vj y(0ng rests against a wall with its feet on horizontal ground x m from t(l0jhw.4 jw0a)1h ry yxdvve7 he wall, as illustrated.
1.Show that the height the ladder reaches up the wall, y, can be expressed by the equation,
$y=\sqrt{36-x^{2}}$
where x is the horizontal distance in metres from the wall to the ladder.
The bottom of the ladder is then pulled away from the wall at a constant speed of 3 m s$^{-1}$.
2.Calculate the speed the top of the ladder is moving down the wall at the instant when the bottom of the ladder is 4m away from the wall.
$\frac{dy}{dx}$≈- .
