Question

1.2+2.3+3.4+....+49.50

Answer 1

Gọi S=1.2+2.3+3.4+...+49.50 3S= 1.2.3+2.3.3+3.4.3+...+49.50.3 3S=1.2.3+2.3.(4-1)+3.4.(5-2)+...+49.50.(51-48) 3S=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+49.50.51-48.49.50 3S=49.50.51 =>S=(49.50.51):3=41650 Có thể mình gõ sai, bạn tự sửa nhé