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<!DOCTYPE html>
<html>
<body>
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<p>单击按钮可显示 PI 和 2*PI 的余弦值。</p>
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<button onclick="myFunction()">试一试</button>
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<p id="demo"></p>
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<script>
function myFunction() {
  var a = Math.cos(Math.PI);
  var b = Math.cos(2 * Math.PI);
  document.getElementById("demo").innerHTML = a + "<br>" + b;
}
</script>
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</body>
</html>
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