Web Forms :: Calling A Function On Master Page From A Content Page?

i have this function on my master page, i want to call it from one of my content page, what should i do?

function showAddress() {
var txtAddress = document.getElementById('txtAddress');
var address = txtAddress.value;
geocoder.getLatLng(
address,
function (point) {
if (!point) {
alert(address + " not found");
}
else {
map.setCenter(point, 15);
var marker = new GMarker(point);
map.addOverlay(marker);
marker.openInfoWindow(address);
}
}
);