td style="text-align:left;">$$f(x) = x^2 - 1$$ (1)</td>
      <td style="text-align:left;"><section class="eqno"><eqn><span class="katex-display"><span class="katex"><span class="katex-mathml"><math><semantics><mrow><mi>f</mi><mo>(</mo><mi>x</mi><mo>)</mo><mo>=</mo><msup><mi>x</mi><mn>2</mn></msup><mo>−</mo><mn>1</mn></mrow><annotation encoding="application/x-tex">f(x) = x^2 - 1</annotation></semantics></math></span><span class="katex-html" aria-hidden="true"><span class="strut" style="height:0.8641079999