Question

Thu gọn  A=1.2 + 2.3+3.4+...+49.50

Answer 1

3A=1.2.3+2.3.3+...+49.50.3

3A=1.2.3-0.1.2+2.3.4-1.2.3+...+49.50.51-48.49.50

3A=49.50.51

3A=124950

A=41650

Answer 2

A=1.2+2.3+3.4+...+49.50

=> 3A= 1.2.3+2.3.(4-1)+3.4.(5-2)+...+49.50.(51-48)

= 1.2.3-1.2.3+2.3.4-2.3.4+...-48.49.50 +49.50.51

=49.50.51

=124950