Please explain how and why ar^k * (1-r)=-ar^(k+1)
Thank you for the help!
Expand the following: a r^k (1-r) = -a r^(k+1)
a r^k (1-r) = a r^k×1+a r^k (-r): a r^k-a r^k r = -a r^(k+1)
a r^k (-r) = a r^(k+1) (-1): Answer: |ar^k+-ar^(k+1) = -ar^(k+1)
