So sánh cặp VCB sau: <span class="katex-r" data-latex="displaystyle α(x) = cs∈(x^2)"></span> và <span class="katex-r" data-latex="displaystyle bη(x) = 1 - cos 2x"></span>, khi <span class="katex-r" data-latex="displaystyle x to 0"></span>