angular router component element not in router-outlet element code example

Example 1: If 'router-outlet' is an Angular component, then verify that it is part of this module.

@NgModule({
  imports: [
      BrowserModule,
      RouterModule

Example 2: router-outlet' is not a known element angular

@NgModule({
  imports: [
      BrowserModule,
      RouterModule
    ],
  exports : [RouterModule]