Question

tinh

A=1.2+2.3+......+99.100

Answer 1

A . 3 = 1.2.3 + 2.3.3 + 3.4.3 + … + 99.100.3 
A . 3 = 1.2.3 + 2.3.(4 - 1) + 3.4.( 5 - 2) + … + 99.100. (101 - 98) 
A . 3 = 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 + … + 99.100.101 - 98.99.100 
A . 3 = 99.100.101 
A = 99.100.101 : 3 
A = 33.100.101 
A = 333 300

Answer 2

A3=1.2.3+2.3.3+3.4.3+.....+99.100.3

A3=1.2.3+2.3.(4-1)+ 3.4.(5-2)+......+99.100(101-98)

A3=1.2.3+2.3.4-1.2.3+2.3.4+3.4.5+......+99.100.101-98.99.100

A3=99.100.101

A=99.100.101:3

A=333300

Answer 3

A=1.2.3+2.3.3+3.4.3+...+99.100.3

A3=1.2.3+2.3(4-1)+3.4(5-2)+......+99.100(101-98)

A3=1.2.3+2.3.4+...+99.100.101-1.2.3+2.3.4+3.4.5+.........+98.99.100

A3=99.100.101

=>A=333300