<div>Изменение Y:
            <input type="text" id="yval" value="от -4 до 4" oninput="verifyY(this.value)"/>
        </div>

        <div>Радиус R:
            <input type="text" id="NAVALNY" value="от 2 до 5" oninput="verifyR(this.value)"/>
        </div>

        <div>
            <button disabled="true" class="indented" type="submit" id="submit" value="Check point">Submit</button>
            <button class="indented" type="reset" value="reset" />
        </div>

        <script type="text/javascript">
            var validY = false;
            var valudR = false;

            function updateSubmit() {
                document.getElementById("submit").disabled = !(validY && validR);
            }
            function verifyY(init) {
                validY = (init*1 >= -4 && init*1 <= 4);
                updateSubmit();
            }
            function verifyR(init) {
                validR = (init*1 >= 2 && init*1 <= 5);
                updateSubmit();
            }
        </script>