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<!DOCTYPE html>
<html>
<head>
<title>Challenge 30</title>
</head>
<body onload="challenge30()">
</body>
</html>
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js
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function challenge30() {
var e = prompt(" Enter expression like 'f(5) = 2x^2 + 3x - 6':"), e = e ? e : 'f(5) = 2x^2 + 3x - 6';
var x = Number(e.slice(e.indexOf("(") + 1, e.indexOf(")")));
var a = Number(e.slice(e.indexOf(" = ") + 3, e.indexOf("x^2")).replace(" ", ""));
var b = Number(e.slice(e.indexOf("^2") + 3, e.indexOf("x ")).replace(" ", ""));
var c = Number(e.substr(e.indexOf("x ") + 2).replace(" ", ""));
var r = a * x * x + b * x + c;
alert(e.slice(0, e.indexOf(" = ") + 3) + r);
}
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