Composite trapezoidal rule illustration
<a href="https://en.wikipedia.org/wiki/User:Oleg_Alexandrov" class="extiw" title="en:User:Oleg Alexandrov">en:User:Oleg Alexandrov</a>
english wikipedia <a class="mw-selflink selflink">Image:Composite_trapezoidal_rule_illustration_small.png</a>