100²-99²+98²-97²+96²-95²+94²-93²+92²-91²
=(100+99)x(100-99)+(98+97)x(98-97)+(96+95)x(96-95)+(94+93)x(94-93)+(92+91)x(92-91)
=100+99+98+97+96+95+94+93+92+91
=(100+91)×10÷2
=955