 Hello and welcome to this session. It is because the following problem today shows that the modulus function f such that from r to r given by fx is equal to mod of x is neither 1 1 not on to where mod of x is x if x is positive or 0 and mod of x is minus x if x is negative. Now here f is not 1 1 for this consider 2 comma minus 2 therefore f of minus 2 is equal to f of 2 but 2 is not equal to minus 2. Now f of x is equal to mod of x takes only non-negative values therefore negative real numbers in co-domain r do not have their images in r which is a domain f is not on to therefore f is not 1 1 and f is not on to. I hope you answered this problem bye and have a nice day.