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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def solidangle(twotheta, sampletodetectordistance, pixelsize=None):
 """Solid-angle correction for two-dimensional SAS images Inputs: twotheta: matrix of two-theta values sampletodetectordistance: sample-to-detector distance pixelsize: the pixel size in mm The output matrix is of the same shape as twotheta. The scattering intensity matrix should be multiplied by it. """

    if pixelsize is None:
        pixelsize = 1
    return sampletodetectordistance ** 2 / np.cos(twotheta) ** 3 / pixelsize ** 2