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## Homework Statement

In David Griffiths Introduction to Quantum Mechanics (2nd ed.), page 32 he normalizes a time independent wave function to get the coefficient A. He dropped the sine part of the integration with no explanation. What is the justification.

## Homework Equations

The time independant wave function given is [itex]\varphi[/itex] = Asin(kx)

Griffiths gets :

[itex]\int^{a}_{0}|A|^{2}sin^{2}(kx) dx = |A|^{2}\frac{a}{2} = 1[/itex]

But:

cos(2kx) = 1 - 2sin[itex]^{2}(kx)[/itex]

and:

sin[itex]^{2}(kx) = \frac{1}{2} - \frac{1}{2}cos(2kx)[/itex]

This means that the integral should really give:

[itex]|A|^{2}(\frac{a}{2} - \frac{1}{4k}sin(2ka))[/itex]

## The Attempt at a Solution

What is the justification for dropping the sine term.