Write the sum in expanded form: sumj=0n-1 (-5)j .
a) 1 - 5 + 25 - 125 +
b) 1 + 5 + 25 + + (-5)n-1
c) 1 - 5 + 25 + + (-5)n-1
d) 1 + 5 - 25 + + (-5)n-1