圆的阴影面积计算

大圆减去小圆，求阴影面积。大圆半径10，小圆半径5.

一.面向对象方法：

$r1=10;

$r2=5;

$mj=3.14*$r1*$r1-3.14*$r2*r2;

echo $mj;

二.面向过程方法：

class yuan

{

public $r;

function __construct(bj)

{

$this->r=$bj;

}

function mianJi()

{

return 3.14*$this->r*$this->r;

}

}

$y1=new yuan(10);

$y2=new yuan(5);

$zmj=$y1->mianJi()-$y2->mianJI();

eccho $zmj;  别忘了输出