) + (-t)*(-t)*(-2*(-s1) - (-t)*(-s1))))&quot;
</pre></div>
<div class="source"><pre class="knitr r"><span class="hl kwd">eval</span><span class="hl std">(</span><span class="hl kwd">parse</span><span class="hl std">(</span><span class="hl kwc">text</span><span class="hl std">=A0),</span> <span class="hl kwd">list</span><span class="hl std">(</span><span class="hl kwc">t</span><span class="hl std">=</span><span class="hl num">0.5</span><span class="hl std">,</span> <span class="hl kwc">s1</span><span class="