discrete math

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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

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