Sempre na hora em que vou chamar o resultado aparece o erro
Eu acho que meu erro está aqui.
$opcao = $_GET['opcao'];
$valor1 = $_GET['valor1'];
$valor2 = $_GET['valor2'];
$total = $_GET['total'];<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "
http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="
http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Calculadora_function</title>
</head>
<?php
$opcao = $_GET['opcao'];
$valor1 = $_GET['valor1'];
$valor2 = $_GET['valor2'];
$total = $_GET['total'];
function calcular($valor1, $valor2, $opcao){
if ($opcao == "somar"){
$total = $valor1 + $valor2;
echo "$total";
}
elseif($opcao == "subtrair"){
$total = $valor1 - $valor2;
echo "$total";
}
elseif($opcao == "multiplicar"){
$total = $valor1 * $valor2;
echo "$total";
}
elseif($opcao == "dividir"){
$total = $valor1 / $valor2;
echo "$total";
}
else
echo "Operação invalida";
}
echo "<img src='calculadora 1.jpg'>";
calcular($valor1 , $valor2 , $opcao)
?>
<body>
<form action="calculadora.php" method="GET">
<tr>
<td><h4>Calculadora</h4></td>
</tr>
<tr>
<td colspan="2"><hr /></td>
</tr>
<tr>
<td>Valor1
<input type="text" name="valor1" id="valor1" size="5" maxlength="5" />
<td><select name="opcao" id="opcao">
<option>Selecione</option>
<option value="somar">+ somar</option>
<option value="subtrair">- subtrair</option>
<option value="multiplicar">* multiplicar</option>
<option value="dividir">/ dividir</option>
</select>
Valor2
<input type="text" name="valor2" id="valor2" size="5" maxlength="5" />
=
<input type="text" name="total" id="total" value="<?php if(isset($total)){ echo $total; } ?>" size="5" maxlength="10"/></td>
</tr>
<tr>
<td><input type="submit" name="igual" id="igual" value="calcular" /> </td>
</tr>
</table>
</form>
</body>
</html>