So sánh cặp VCB sau: <span class="katex-r" data-latex="displaystyle α(x) = e^{ac{1}{x}} - cos(ac{1}{x}right) - ac{1}{x}"></span>, <span class="katex-r" data-latex="displaystyle bη(x) = ac{1}{x}"></span> khi <span class="katex-r" data-latex="displaystyle x to +∞"></span>