Question

tính tổng 

P = 1.2 + 2.3 + 3.4+....+ 99.100

Answer 1

3P= 1.2.3+2.3.3+3.4.3+...+99.100.3

3P= 1.2.3+ 2.3.(4-1)+3.4.(5-2)+...+99.100.(101-98)

3P= 1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+99.100.101-98.99.100

3P= 99.100.101

P= 33.100.101= 333300

Answer 2

3P=1.2.3+2.3.(4-1)+3.4.(5-2)+............+99.100.(101-98)

3P=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+..........+99.100.101-98.99.100

3P=99.100.101

P=99.100.101:3

P=333300

Answer 3

3P= 1.2.3+2.3.3+3.4.3+...+99.100.3

3P= 1.2.3+2.3.(4-1)+3.4.(5-2)+...+99.100.(101-98)

3P= 1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+99.100.101-98.99.100

3P= 99.100.101

P=33.100.101=333300

Answer 4

333300

Answer 5

ta co: 3P=1.2.3+2.3.3+3.4.3+...+99.100.3

         3P=1.2.3+2.3.(4-1)+3.4+(5-2)+...+99.100.(101-98)

         3P=1.2.3+2.3.4-1.2.3+...+99.100.101-98.99.100

        3P=99.100.101

       P=33.100.101=333300

Answer 6

Đặt S= 1.2 + 2.3 + 3.4 + ...+ 99.100
 3S = 1.2.3+2.3.3+3.4.3+...+98.99.3+99.100.3
3S= 1.2.3+2.3(4-1)+3.4(5-2)+...+98.99(100-97)+99.100(101-98)
3S= 1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...-97.98.99+99.100.101-98.99.100
3S = 99.100.101  3S = 3.33.100.101 
 S=33.100.101= 333300