# Does this look familiar?

Calculus Level 4

$\large \int_{-\infty}^{\infty} \left( \dfrac{e^{\frac{-x^2}{2}}}{\sqrt{2\pi}} \right) dx$

If the value for the above integral is $$A$$, find the value of $$b$$ such that

$\large \int_{-b}^{b} \left( \dfrac{e^{\frac{-x^2}{2}}}{\sqrt{2\pi}} \right) dx = 0.9A$.

Give the answer to the nearest 3 decimal places.

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