Question

Tinh: 1000²-999²+998²-997²+996²-995²+...+4²-3²+2²-1².

Answer 1

= (1000 - 999).(1000 + 999) + (998 - 997).(998 + 997) + ....+ (4 - 3).(4 +3) + (2 - 1) .(2+1)

= 1000 + 999 + 998 + 997 + ..+4+3+ 2+1

= (1000 +1).1000 : 2 = 500 500

Answer 2

 1000²-999²+998²-997²+996²-995²+...+4²-3²+2²-1².

= (1000 - 999).(1000 + 999) + (998 - 997).(998 + 997) + ....+ (4 - 3).(4 +3) + (2 - 1) .(2+1)

= 1000 + 999 + 998 + 997 + ..+4+3+ 2+1

= (1000 +1).1000 : 2

= 500 500

hok tốt