ss="special">+</span> <span class="identifier">x</span><span class="special">[</span><span class="number">0</span><span class="special">]</span> <span class="special">*</span> <span class="identifier">pert</span><span class="special">[</span><span class="number">1</span><span class="special">]</span> <span class="special">-</span> <span class="identifier">b</span> <span class="special">*</span> <span class="identifier">pert</span><span class="special">[</span><span class="number">2</span><span class="specia