How to check IsUserInRoles

I have a code below, doesn't work, Kindly help us.
.

$core_v2_roleUsers.IsUserInRoles($userName, $roleNames)


#set($roleNames= [])
$roleNames.Add('Administrators')

$core_v2_roleUsers.IsUserInRoles('sakthivelE',$roleNames)

I need an example code or guide us.