I created a new Angular 5 project. After that I followed instructions given on Angular CLI GitHub page to use Bootstrap 4.0.0 with Angular 5.2.2. I use \'npm install bootstrap\'
Bootstrap has dependency on popper and jquery. It is always a good idea to install these modules along with bootstrap.
npm install --save bootstrap@4 jquery@version popper@version
using --save adds these dependencies in your package.json.
Then you can go to angular.json (Angular 6 and cli v6) or angular-cli.json (Angular 5 or below and cli v1.7) and paste the css of bootstrap in node modules under styles array. And add jquery, popper and bootstrap.js files under scripts.
Hope that helps!