## Thomas' Calculus 13th Edition

Beacuse $a_{n}=2+(-1)^{n},$ so $$a_{1}=2+(-1)^{1}=2-1=1$$ $$a_{2}=2+(-1)^{2}=2+1=3$$ $$a_{3}=2+(-1)^{3}=2-1=1$$ $$a_{4}=2+(-1)^{4}=2+1=3$$