Dragomir, S. S., and N. M. Ionescu. “A New Refinement of Jensen’s Inequality”. Anal. Numér. Théor. Approx., vol. 20, no. 1, Aug. 1991, pp. 39-41, https://ictp.acad.ro/jnaat/journal/article/view/1991-vol20-nos1-2-art5.