4B=1.2.3.4+2.3.4.4+...+(n-1)n(n+1).4
=1.2.3.4-0.1.2.3+2.3.4.5-1.2.3.4+...+(n-1)n(n+1)(n+2)-[(n-2)(n-1)n(n+1)]
=(n-1)n(n+1)(n+2)-0.1.2.3=(n-1)n(n+1)(n+2)
=>B=(n-1)n(n+1)(n+2)/4
k nha
Tính B = 1.2.3.4 + 2.3.4.4 +...+ (n - 1)n(n+1)
TINH
B=1.2.3.4+2.3.4.4+....+(n-1)n(n+1).4
hung ui GIAI HO TI
KO GIẢI ĐC MAI LÊN LỚP SẼ BIẾT
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Hơi khó, giúp mình với
A= 1,2+ 2,3+ 3,4+ ....+ n.(n+1)
B= 1.2.3+ 2.3.4.4+ ...+ (n-1)n(n+1).4
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
Cho n!=1.2.3.4.....n. Chứng minh \(\frac{5}{3}<\frac{1}{1!}+\frac{1}{2!}+...+\frac{1}{2016!}<2\)
CM:
1+\(\frac{1}{1.2}+\frac{1}{1.2.3}+\frac{1}{1.2.3.4}+...+\frac{1}{1.2.3...n}< 2\)
Tính :
\(A=\left(1-\frac{1}{1.2}\right)\left(1-\frac{1}{1.2.3}\right)\left(1-\frac{1}{1.2.3.4}\right)...\left(1-\frac{1}{1.2.3.4.....1986}\right)\)
\(\text{Tính tổng: }\dfrac{1}{1.2.3.4}+\dfrac{1}{2.3.4.5}+\dfrac{1}{3.4.5.6}+...+\dfrac{1}{27.28.29.30}\)
CMR : 1+ \(\frac{1}{1.2}\)+\(\frac{1}{1.2.3}\)+\(\frac{1}{1.2.3.4}\)+.....+\(\frac{1}{1.2.3.....n}\)< 2
