pan class="w"> </span><span class="o">+</span><span class="w"> </span><span class="n">xr</span><span class="p">(</span><span class="n">ix</span><span class="p">)</span><span class="o">*</span><span class="n">yr</span><span class="p">(</span><span class="n">iy</span><span class="p">)</span><span class="w"> </span><span class="o">-</span><span class="w"> </span><span class="n">xi</span><span class="p">(</span><span class="n">ix</span><span class="p">)</span><span class="o">*</span><span class="n">yi</span><sp