Because, I is an ideal, if n is there, every 2 times n is there, 3 times n is there, minus n is there, minus 2 times n is there.
ఎందుకంటే, I ఐడియల్ , n ఉంటే, ప్రతి 2 * n ఉంటుంది, 3 * n ఉంది, - n ఉంది, - 2 * n ఉంటుంది.