Question

B=1.2.3+2.3.4+3.4.5+......+98.99.100

Giúp mk nha đến 4h mk phải đi học rồi!

Answer 1

4B = 1.2.3.4+ 2.3.4.4+ 3.4.5.4 +....+ 97.98.99+98.99.100.4

     = 1.2.3.4 + 2.3.4.(5-1) + 3.4.5.(6-2)+...+97.98.99.(100-96)+ 98.99.100.(101-97) 

=1.2.3.4 +2.3.4.5-1.2.3.4+3.4.5.6-2.3.4.5+ ...+97.98.99.100-96.97.98.99+ 98.99.100.101-97.98.99.100

4B= 98.99.100.101 ( rút gọn hết còn lại 98.99.100.101)

 B = 98.99. 100.101: 4 = .....( Bạn tự tính nhé)

 

Answer 2

B=1.2.3+2.3.4+3.4.5+.......+98.99.100

4b=4.(1.2.3+2.3.4+3.4.5+......+98.99.100)

=1.2.3.4+2.3.4.4+3.4.5.4+.....+98.99.100.4

=1.2.3.4+2.3.4.(5-1)+3.4.5.(6-2)+......+98.99.100.(101-97)

=1.2.3.4+2.3.4.5-1.2.3.4.+.....+98.99.100.101-97.98.99.100

=(1.2.3.4-1.2.3.4)+(2.3.4.5-2.3.4.5)+.....+(97.98.99.100-97.98.99.100)+98.99.100.101

B=\(\frac{98.99.100.101}{4}\)

B=24 497 550