# Translations:Reflection and refraction – book/11/en

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Thus, *AC* is equal to *DB* times . The wavelet at *B* has a radius of zero. Because the line *BC* is tangent to all the wavelets, it constitutes their envelope. Therefore, *BC* represents a refracted wavefront in the lower medium. Line *BC* is tangent to the circular wavelet *MCN* at the point *C*, and therefore it is perpendicular to the radius *AC*. It follows that *AG* is a refracted ray associated with the refracted wavefront *BC*. Now in triangle *BAD*, we have