a(n)=[1+(-1)^n]^(1/2)
a(n)=[1+(-1)^n]√2/2
a(n)=√2*|sin[(n-1)π/2]|
a(n)=√2*sin^2[(n-1)π/2]
a(n)=√2*|cos(nπ/2)|
a(n)=√2*cos^2(nπ/2)
……