Lời giải:
$A=10(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+...+\frac{1}{92.93.94.95})$
$3A=10(\frac{4-1}{1.2.3.4}+\frac{5-2}{2.3.4.5}+...+\frac{95-92}{92.93.94.95})$
$=10(\frac{1}{1.2.3}-\frac{1}{2.3.4}+\frac{1}{2.3.4}-\frac{1}{3.4.5}+...+\frac{1}{92.93.94}-\frac{1}{93.94.95})$
$=10(\frac{1}{1.2.3}-\frac{1}{93.94.95})$
$A=\frac{10}{3}(\frac{1}{1.2.3}-\frac{1}{93.94.95})$
A= 10/1.2.3.4+10/2.3.4.5+...+10/92.93.94.95
\(\text{Tính tổng: }\dfrac{1}{1.2.3.4}+\dfrac{1}{2.3.4.5}+\dfrac{1}{3.4.5.6}+...+\dfrac{1}{27.28.29.30}\)
1, Tính giá trị biểu thức
P= 1.2.3.4+2.3.4.5+3.4.5.6+4.5.6.7+...+97.98.99.100
tính\(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+...+\frac{1}{27.28.29.30}\)
Tính :
\(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+......+\frac{1}{17.18.19.20}\)
Tính tổng : A = \(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+\frac{1}{3.4.5.6}+...+\frac{1}{98.99.100.101}\)
\(c=\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+\frac{1}{3.4.5.6}+...+\frac{1}{98.99.100.101}\)= ?
bai1 1.2.3.4+ 2.3.4.5+......+( n-2).(n-1).n.(n+1)
bai 2 D= 1^4+ 2^4+.....+ n^4
\(\frac{1}{1.2.3.4}+\frac{1}{2.3.4.5}+\frac{1}{3.4.5.6}+...+\frac{1}{200.201.202.203}\)
tính tổng trên
