You need to specify the path correctly for the css,js files as following:
WebView webView = (WebView)findViewById(R.id.webView1);
WebSettings webSettings = webView.getSettings();
webSettings.setJavaScriptEnabled(true);
String path="file:///android_asset/";
String js = "<html><head>"
+ "<link rel='stylesheet' href='"+path+"jqmath-0.4.0.css'>"
+ "<script src='"+path+"jquery-1.4.3.min.js'></script>"
+ "<script src='"+path+"jqmath-etc-0.4.0.min.js'></script>"
+ "</head><body>"
+ "<script>var s = '$ax^2+bx+c=0$ with $a≠0$';M.parseMath(s);document.write(s);</script></body>";
webView.loadData(js, "text/html", "UTF-8");
note that the files should be in assets folder.