You can use trial and error to work this out.
Just sub in points
1. choose r to be odd and see what you obtain : )
If r is an integer greater than 1, what is the value of (−1)^r +1 if:
1. r is an odd integer
2.r is an even integer
3 answers
(-1)^odd integer = -1
(-1)^even integer = +1
so you have either
-1 + 1 =
or
1 + 1=
(-1)^even integer = +1
so you have either
-1 + 1 =
or
1 + 1=
thanks