Lời giải:
$A=1+\frac{1}{2^2}+\frac{1}{3^2}+....+\frac{1}{50^2}$
$< 1+\frac{1}{1.2}+\frac{1}{2.3}+....+\frac{1}{49.50}$
$=1+1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+....+\frac{1}{49}-\frac{1}{50}$
=2-\frac{1}{50}< 2$
(đpcm)
CMR A<2
A=1/1^2+1/2^2+1/3^2+.....+1/50^2
A, CHO A= 1/12+1/22+1/23+...+1/502 CMR A<2
B,CHO B= 21+22+23+...+230 CMR B CHIA HẾT CHO 21
GIÚP TUI LIỀN NHA VÌ TUI CẦN GẤP
cho A = 1/3 mũ 2 + 1/4 mũ 2 + 1/5 mũ 2 + ...+ 1/50 mũ 2 CMR : A > 1/4
giúp mình nhé
Bài 1 : Cho A = \(\frac{1}{^{1^2}}+\frac{1}{2^2}+\frac{1}{3^2}+\frac{1}{4^2}+...+\frac{1}{50^2}\) . CMR : A < 2
Bài 2 : Cho B = \(2^1+2^2+2^3+2^4+...+2^{30}\). CMR : B chia hết cho 21
CMR: A=1+1/2^2+1/3^2+1/4^2+...+1/50^2>2
bài 6:
cho : A= 1/12+1/22+1/32+1/42+...+1/502
CMR: A<2
cho A = 1/3 mũ 2 + 1/4 mũ 2 + 1/5 mũ 2 + ...+ 1/50 mũ 2 CMR : A1/4
Cho A = 1 + 1/2 = 1/3 + 1/4 + ... + 1/2^100 -1
CMR : a) A < 100
b) A > 50
Cho a = 1+1/2+1/3+1/4+.....+1/(2100-1)
CMR P > 50