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Vosnian
Answers (1)
r ^ 2 - 1 = ( r + 1 ) * ( r - 1 ) ( r ^ 2 - 1 ) / ( r + 1 ) ^ 2 = [ ( r + 1 ) * ( r - 1 ) ] / [ ( r + 1 ) * ( r + 1 ) ] = ( r - 1 ) / ( r + 1 )
