[填空题]
A piece of jewellery is being designed for an auction. ;t x+6 q5nhowkqrmnx6,t +k,xvn3v4.tfjjok-ys9*q 6c2 vv lIts shape is based on the graly*.vsn4jfk t-co23 vjvq9 v6ph of
$y=\frac{x}{50} \sqrt{625-x^{2}} \quad \text { for } 0 \leq x \leq 25$
which is revolved $360^{\circ}$ about the x -axis, where x and y are measured in $\mathrm{mm}$ .
1. Find the area bounded by the graph and the x -axis.
Area ≈ .
2. Hence or otherwise, find the volume of the jewel is(≈) mm$^3$.
3. If $1 \mathrm{~cm}^{3}$ of silver weighs 10.5 grams, and 1 gram of silver costs $\$ 1.50$ , find the cost of the silver used for the jewel to the nearest dollar is(≈) .
