Cho các dãy số <span class="MathJax_Preview" style="color: inherit;"><span class="MJXp-math" id="MJXp-Span-1"><span class="MJXp-mstyle" id="MJXp-Span-2"><span class="MJXp-mo" id="MJXp-Span-3" style="margin-left: 0em; margin-right: 0em;">(</span><span class="MJXp-msubsup" id="MJXp-Span-4"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-5" style="margin-right: 0.05em;">u</span><span class="MJXp-mi MJXp-italic MJXp-script" id="MJXp-Span-6" style="vertical-align: -0.4em;">n</span></span><span class="MJXp-mo" id="MJXp-Span-7" style="margin-left: 0em; margin-right: 0em;">)</span><span class="MJXp-mo" id="MJXp-Span-8" style="margin-left: 0em; margin-right: 0.222em;">,</span><span class="MJXp-mspace" id="MJXp-Span-9" style="width: 0.167em; height: 0em;"></span><span class="MJXp-mo" id="MJXp-Span-10" style="margin-left: 0em; margin-right: 0em;">(</span><span class="MJXp-msubsup" id="MJXp-Span-11"><span class="MJXp-mi MJXp-italic" id="MJXp-Span-12" style="margin-right: 0.05em;">v</span><span class="MJXp-mi MJXp-italic MJXp-script" id="MJXp-Span-13" style="vertical-align: -0.4em;">n</span></span><span class="MJXp-mo" id="MJXp-Span-14" style="margin-left: 0em; margin-right: 0em;">)</span></span></span></span><script type="math/tex" id="MathJax-Element-1">\large (u_n),\, (v_n)</script> và $\large \lim\, u