# Engineering Tables/Normal Distribution/Tail Function Graph

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The tail function is the area under the normal distribution N(0,1) between x and +∞:

${\displaystyle {\mbox{T}}(x)=\int \limits _{x}^{\infty }{{1 \over {\sqrt {2\pi }}}\exp \left({-{{y^{2}} \over 2}}\right)dy}}$

For x > 6.5, the tail function can be approximated as:

${\displaystyle {\mbox{T}}(x)={1 \over {x{\sqrt {2\pi }}}}\exp \left({-{{x^{2}} \over 2}}\right)}$