1000²/(252²-248²)
=1000²/(252-248)(252+248)
=1000²/(2*500)
=1000²/1000
=1000
199×201/100²
=(200-1)(200+1)/100²
=(200²-1)/100²
=200²/100²-1/100²
=4-1/10000
=39999/10000
1000²/(252²-248²)
=1000²/(252-248)(252+248)
=1000²/(2*500)
=1000²/1000
=1000
199×201/100²
=(200-1)(200+1)/100²
=(200²-1)/100²
=200²/100²-1/100²
=4-1/10000
=39999/10000