xxxxxxxxxx
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>大卫编程网(div.cn)</title>
</head>
<body>
<math xmlns="http://www.w3.org/1998/Math/MathML">
<mrow>
<mrow>
<msup>
<mi>x</mi>
<mn>2</mn>
</msup>
<mo>+</mo>