Question

[Trần Hoàng Phương Anh]

A=1x2+2x3+3x4+...+49x50

B=1x3+3x5+5x7+...+99x101

C=1x2x3+2x3x4+3x4x5+...+50x51x52

D=1x4+2x5+3x6+...+60x63

E=1x1+2x2+3x3+...+50x50

F=1x1+3x3+5x5+...+71x71

G=1x1+4x4+7x7+...+100x100

I=1x2x3+3x4x5+5x6x7+...+69x70x71

Answer 1

[VRCT_Ran Love Shinichi]

A=1x2+2x3+3x4+...+49x50

3A= 3(1.2+2.3+3.4+...+49.50)

3A= 1.2.3+2.3.3+3.4.3+...+49.50.3

3A= 1.2.(3-0)+2.3(4-1)+3.4(5-2)+...+49.50.(51-48)

3A= 0.1.2-1.2.3+1.2.3-2.3.4+2.3.4-3.4.5+...+48.49.50-49.50.51

3A= 49.50.51

A= 49.50.51/3=41650

Answer 2

[VRCT_Ran Love Shinichi]

B=1x3+3x5+5x7+...+99x101

B=1/1.3 +1/3.5 +...+1/99.101

2B=2/1.3 + 2/3.5 +...+2/99.101

2B=1-1/3+1/3-1/5+...+1/99-1/101

2B=1-1/101

2B=100/101

B=100/101:2=100/202