hi I  have textbox and RequiredFieldValidator and checkbox in my page

put textbox and RequiredFieldValidator in div

   <div class="CGM2_1">
                                <div class="CGM2_121">

                                    <asp:TextBox ID="Txtprice" runat="server" CssClass="Txtprice1"></asp:TextBox>
                                </div>
                                <asp:Label ID="Label27" runat="server" CssClass="lblprice1"><span style="color:Red">*&nbsp&nbsp</span>قیمت:</asp:Label>
                                <asp:RequiredFieldValidator ID="RequiredFieldValidator5" runat="server" ErrorMessage="price"
                                    ControlToValidate="Txtprice" Display="None" Enabled="false"></asp:RequiredFieldValidator>

                            </div>

and make RequiredFieldValidator Enabled="false"

 when users checked checkbox it show Div

below is code:

   <script type="text/javascript">
        function ShowHideDiv(CHBPrice) {
            var CGM2_1 = document.getElementById("CGM2_1");
            CGM2_1.style.display = CHBPrice.checked ? "block" : "none";
        }
    </script>

now I want when users checked checkbox it does:

 RequiredFieldValidator Enabled="true"

how I can do it in above code?

Best Regards

Neda