The multiplicative inverse is just the reciprocal of the number. The reciprocal is just " flipping " the number. So the reciprocal of 3 (or 3/1) is 1/3. And any time u multiply a number by its multiplicative inverse (reciprocal), the result is 1
3 * 1/3 = 3/3 = 1.....so N is ur multiplicative inverse
