Ta có : \(A=\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+.....+\frac{1}{2^n}\)
\(\Rightarrow2A=1+\frac{1}{2}+\frac{1}{2^2}+.....+\frac{1}{2^{n-1}}\)
\(\Rightarrow2A-A=1-\frac{1}{2^n}\)
\(\Rightarrow A=1-\frac{1}{2^n}\)
\(\Rightarrow A=\frac{2^n}{2^n}-\frac{1}{2^n}=\frac{2^n-1}{2^n}\)
a,(x+2) (y+1)=23
chia ra truong hop cho minh cai
b,(n+5) chia hết cho n-2
cai này cũng chia ra truong hop
c,2n+1 chia hết cho n-5
chia ra truong hop
Tinh gia tri cua cac bieu thuc sau bang cach hop li
a) 125 : (-61) . (-23) . (-1) 2n
b) 136 . (-47) + 36 . 47
Tinh hop ly cac gia tri bieu thuc sau
a) \(4\frac{8}{23}+5\frac{7}{8}-9\frac{8}{23}\)
b)\(6\frac{3}{8}+5\frac{1}{2}\)
tinh hop ly a=1/1*2+1/2*3+...+1/9*10
Tinh bang cach hop li
1/2+1/4+1/8+1/16+1/32
1/2+1/4+1/16+.....+1/100000
tinh cac tong sau 1 cach hop li
tinh hop li A = 1*2+2*3+.................+n* (n+1)
thuc hien phep tinh sau 1 cach hop li
9764/36615+36.85.20/25.84.34+22/10+3 19/133(la hon so)
b, 4/6+4/30+4/70+..+4/2.99.101
tap hop cac UC 2n+1 va 3n+1
Tinh hop ly:
(1+2^4+2^8) : (1+2+2^2+...+2^11)
