6.2Exponential Functions

Part (b) of the cobalt-60 example plugs a given t directly into Nₜ/N₀ = e^(−λt) to get a fraction remaining (0.138) — a plain forward evaluation of an exponential function at a value of the input, the move 6.2 teaches, distinct from part (c) of the same example which instead solves the equation for t (already bridged to §6.7).