=13+33+53+73+93−(23+43+63+83)
=Sum of cubes of first 5 odd number -Sum of cubes of first 4 even number
=n2(2n2–1)−2n2(n+1)2
=1225–800
=425
The sum of the series 13 - 23 + 33 - 43 + ....... + 93 is: