A geometric proof that for 0<r<1, (1-r) + (1-r)r + (1-r)r² + … = 1, and therefore that 1 + r + r² + … = 1/(1 – r) pic.twitter.com/r22dM7PoUM

— Andrew M. Webb (@AndrewM_Webb) October 8, 2019

The greater/less-than symbols (> and <) were introduced by the British mathematician Thomas Harriot in 1631. It then took 103 years for the French scientist Pierre Bouguer to introduce the greater/less-than or equal to symbols (≥ and ≤) for the first time. pic.twitter.com/ppzqaEP0dM

— Fermat's Library (@fermatslibrary) October 9, 2019