[填空题]
A ladder that is 6 m long rests against a wall with its feet6b*btnh1 hz t7xu s -sb-q wx1-l3gxo/e1f lng+l(kd; on horizontal ground x m fr kb3gws;d(xs1 nl g-xq+ u /l-l-xo1feom the 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.
$\frac{dy}{dx}$≈- .
