Richard Feynman (Nobel Physicist) proved it in high school using a **funny** Calculus: “Differentiating under Integral” — is it legitimate to do so ? Of course it is by “The Fundamental Theorem of Calculus”

**Note**: We were thought in high school the “*HOW*” of calculating (such as integration and differentiation), but not the “*WHY*” (the Theorem behind). Richard Feynman was unique in exploring the WHY since high school, it helped later he was assigned by President Reagan to investigate the 1986 ‘Challenger’ disaster ?