An interesting integral: $latex \int_0^\infty e^{-6t}dt$

An interesting integral: \int_0^\infty e^{-6t}dt.

This is the problem on Mathematics of

The solution of Dror helps us learn the following trick: de^y = e^y.dy \Rightarrow dy = \dfrac{de^y}{e^y}. So \int_{-\infty}^xe^{y}dy=\int_{-\infty}^xde^{y}=e^x- \lim_{y \to -\infty}e^y=e^x-0=e^x.

Dror’s solution:
So, by substituting y=-6t, we can use this propety. We calculate:
dt=-\frac{1}{6}dy, 0 \to0,\infty \to - \infty

The integral then becomes:
\int_0^\infty e^{-6t}dt=\int_0^{-\infty}-\frac{1}{6}e^{y}dy=\frac{1}{6}\int_{-\infty}^0e^{y}dy=\frac{1}{6}*e^0=\frac{1}{6}*1=\frac{1}{6}


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