4 ms·

Actually, this method was already used by Leibniz, although it was not that common at Feynman's time. https://en.wikipedia.org/wiki/Leibniz_integral_rule https

• alisonkisk 5y ago
  Yes, that's the first sentence of the main article body. > Today’s article is going to discuss an obscure but powerful integration technique most commonly known as differentiation under the integral sign, but occasionally referred to as “Feynman’s technique” due to his popularization of this technique in his book, and properly known as the Leibniz Integral Rule.