Explain why the ether obtained by treating an optically active alcohol with PBr₃ followed by sodium methoxide has the same configuration as the alcohol, whereas the ether obtained by treating the alcohol with tosyl chloride followed by sodium methoxide has a configuration opposite that of the alcohol.

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CH3 CH3 1. PBr3/pyridine R OH R "OCH3 H 2. СH,0 H CH3 CH3 1. TsCl/pyridine CH;O" H R VOH R 2. CH;0 H