E= (1/12 + 1) x (1/13 +1) x (1/14 + 1) x ... x (1/199 +1 )
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Ta có 13x = \(\frac{13^{17}+13}{13^{17}+1}=1+\frac{12}{13^{17}+1}\)
13y = \(\frac{13^{16}+13}{13^{16}+1}=1+\frac{12}{13^{16}+1}\)
Vì 1317 + 1 > 1316 + 1
=> \(\frac{1}{13^{17}+1}< \frac{1}{13^{16}+1}\)
=> \(\frac{12}{13^{17}+1}< \frac{12}{13^{16}+1}\)
=> \(1+\frac{12}{13^{17}+1}< 1+\frac{12}{13^{16}+1}\)
=> 13x < 13y
=> x < y
Vậy x < y
\(A=\left(1-\frac{1}{15}\right)\left(1-\frac{1}{21}\right)\left(1-\frac{1}{28}\right)...\left(1-\frac{1}{79800}\right)\)
\(A=\frac{14}{15}.\frac{20}{21}.\frac{27}{28}...\frac{209}{210}\)
\(A=\frac{28}{30}.\frac{40}{42}.\frac{54}{56}...\frac{418}{240}\)
\(A=\frac{4.7}{5.6}.\frac{5.8}{6.7}.\frac{6.9}{7.8}...\frac{19.22}{20.21}\)
\(A=\frac{4.5.6...19}{5.6.7...20}.\frac{7.8.9...22}{6.7.8...21}\)
\(A=\frac{4}{20}.\frac{22}{6}\)
\(A=\frac{11}{15}\)
TA có 13-13*1+10-10= 13- 13+10-10=0+0=0
(10*11+12*13+14*15+...+22*23+24*25)*0=0
* là dấu x nhe bạn
thick minh nha
( 10 x 11 + 12 x 13 + 14 x 15 + ... + 22 x 23 + 24 x 25) x ( 13 - 13 x 1 + 10 -10)
= ( 10 x 11 + 12 x 13 + 14 x 15 + ... + 22 x 23 + 24 x 25) x 0
= 0
k cho anh nha !!!!!!!!!!!!!!!! : học lớp 5 rùi
a) \(\dfrac{1}{7}< \dfrac{x}{35}< \dfrac{2}{5}\)
\(\Rightarrow\dfrac{5}{35}< \dfrac{x}{35}< \dfrac{14}{35}\)
\(\Rightarrow5< x< 14\)
b) \(\dfrac{5}{13}< 2-x< \dfrac{5}{8}\)
\(\Rightarrow2-\dfrac{5}{8}< x< 2-\dfrac{5}{13}\)
\(\Rightarrow\dfrac{11}{8}< x< \dfrac{21}{13}\)
E=13/12.14/13....200/199=200/12=50/3