Dropdown From Bootstrap Menu Not Descending

I'm sorry to go back to the Bootstrap dropdown issue, but I've seen all the related questions and I could not solve my problem.

I do not understand almost anything about JavaScript, and I'm using the newer version of Bootstrap (version 4).

The browser console is displaying the following errors: Uncaught ReferenceError: $ is not defined bootstrap.min.js: sourcemap: 6 Uncaught ReferenceError: Popper is not defined bootstrap.js: 3849 Uncaught ReferenceError: Popper is not defined

My HTML code menu:

         @ ViewBag.Title          

<div class="row">
    <div class="col-md-4">
        <img height="110" src="~/Content/Imagens/Logo-Prefeitura-De-Araguaina (1).png" />
    </div>
    <div class="col-md-6" style="margin-top: 1em;">
        <h2>Gestor Rodoviário de Araguaína</h2>
    </div>
    <div class="col-md-2 d-md-flex justify-content-md-end" style="margin-top: 1em;">
        <p>Olá, @Session["nomeUsuario"]!</p>
    </div>
</div>
<div class="row">
    <div class="col-md-12 d-md-flex justify-content-md-end col-lg-12 d-lg-flex justify-content-lg-end" style="margin-top: -1.5em;">
        <a style="margin-top: -3em;" href="@Url.Action("Logout", "Usuario")">sair</a>
    </div>
</div>







<nav class="navbar navbar-expand-lg navbar-dark bg-dark">
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
    </button>

    <div class="collapse navbar-collapse" id="navbarSupportedContent">
        <ul class="navbar-nav mr-auto">
            <li class="nav-item active">
                <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
            </li>
            <li class="nav-item">
                <a class="nav-link" href="#">Link</a>
            </li>
            <li class="nav-item dropdown">
                <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
                    Dropdown
                </a>
                <div class="dropdown-menu" aria-labelledby="navbarDropdown">
                    <a class="dropdown-item" href="#">Action</a>
                    <a class="dropdown-item" href="#">Another action</a>
                    <div class="dropdown-divider"></div>
                    <a class="dropdown-item" href="#">Something else here</a>
                </div>
            </li>
            @*<li class="nav-item">
                <a class="nav-link disabled" href="#">Disabled</a>
            </li>*@
        </ul>
        @*<form class="form-inline my-2 my-lg-0">
            <input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
            <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
        </form>*@
    </div>
</nav>

<script>
      $(function () {
        $('.dropdown-toggle').dropdown();
      });
</script>


<script type="text/javascript" src="~/scripts/js/jquery-1.9.1.js"></script>
<script type="text/javascript" src="~/scripts/js/bootstrap.min.js"></script>
<script type="text/javascript" src="~/scripts/js/bootstrap.js"></script>


<div>
    @RenderBody()
</div>