Question

[Vân Hồng]

                                    Ghi lời giải đầy đủ nhé cảm ơn ạ

Tính nhanh : 

a,      A= 1 + 4 + 16 + 64 + .........+ 16384 + 65536 

b,     B= 1/2  + 1/4 + 1/8 + 1/16 + ..........+ 1/128 + 1/256 

c,     C= 4/1x5 + 4/5x9 + 4/8x13 +...........+ 4/81/85 + 4/81x89

d,     D= 1/1x4 + 1/4x7 + 1/7x10 + ..........+ 1/301x304 + 1/304x307

e,     E= 1/2 + 1/6 + 1/12 + 1/20 + 1/30 +........+ 1/110 + 1/132 

g,     G= 2/1x6 + 2/6x11 + 2/11x16 + 2/16x21+........+ 2/91x96 + 2/96x101

Answer 1

[Nguyễn Lê Phước Thịnh]

a: 4A=4+4^2+...+4^9

=>3A=4^9-1

=>A=(4^9-1)/3

b: 2A=1+1/2+...+1/2^7

=>A=1-1/256=255/256

c: =1-1/5+1/5-1/9+...+1/85-1/89

=1-1/89=88/89

d: =1/3(3/1*4+3/4*7+...+3/304*307)

=1/3(1-1/4+1/4-1/7+...+1/304-1/307)

=1/3*306/307=102/307

e: E=1-1/2+1/2-1/3+...+1/11-1/12

=1-1/12=11/12

g: =2/5(1-1/6+1/6-1/11+...+1/96-1/101)

=2/5*100/101=40/101