# discrete math

posted by
**thisha**
.

1. let A and B be sets. Show that

A U (B - A)=A U B

2. determine whether f is a function from Z to R if

a) f(n)= +n

b) 1/(n square -4)

For 1. B-A is the same as B intersect ~A (That's the complement of A)

So A U B = A U (B int ~A) = (A U B) int (A U ~A) A U ~A is the universal set.

For 2. a) f(n) is the absolute value function, so yes, it's a function.

For 2. b) 1/(n^2 - 4) f is not defined at +/- 2