Dragomir, S. S. “Improvements of Ostrowski and Generalised Trapezoid Inequality in Terms of the Upper and Lower Bounds of the First Derivative”. Tamkang Journal of Mathematics 34, no. 3 (September 30, 2003): 213-222. Accessed October 28, 2021. https://journals.math.tku.edu.tw/index.php/TKJM/article/view/312.