Question

SHOW THAT
A={n(-1)^n-1 ;n is element of N(natural number) } IS COUNTABLE.

Answer 1

\[n \times(-1)^{n-1}\rightarrow 1,-2,+3,-4,-5,+6,-7,...\]
is this
if yes
it is sufficient to find a bijective function between N and A
so the simplest idea is f(n)=n(-1)^(n-1)

Answer 2

IF A=Z And B=N Show that A~B

i denfine
but sir still say it was wrong