20: 11/12
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`A=(20^10+1)/(20^11+1)`
`=>20A=(20^11+20)/(20^11+1)=1+19/(20^11+1)`
Hoàn toàn tương tự: `20B=1+19/(20^12+1)`
Vì `19/(20^12+1)<19/(20^11+1)`
`=>20B<20A`
`=>B<A`
( 7/20 + 11/15 - 15/12 ) : ( 11/20 - 26/45 )
= -1/6 : -1/36
= -5/36
a: \(=\dfrac{20\left(1-12\right)}{30\left(-1-10\right)}=\dfrac{2}{3}\)
b: \(=\dfrac{11^9\cdot3^{18}}{3^{18}\cdot11^{11}}=\dfrac{1}{121}\)
a: \(=\dfrac{20\left(1-12\right)}{30\left(-1-10\right)}=\dfrac{20}{30}=\dfrac{2}{3}\)
b: \(=\dfrac{11^9\cdot3^{18}}{3^{10}\cdot11^{11}\cdot3^8}=\dfrac{1}{121}\)
a)11+11+11+11+11+11+11+11+11=\(11^9\)=99.
b)56+56+12+12+12+20+56+56+56=56+56+56+56+56+56=\(56^6\)=336.
c)\(45^8\)=360.
d)\(12^4\)=48
a)11+11+11+11+11+11+11+11+11=\(11^9\)=99.
b)56+56+12+12+12+20+56+56+56=56+56+56+56+56+56=\(56^6\)=336.
c)\(45^8\)=360.
d)\(12^4\)=48
\(\left(\frac{7}{20}+\frac{11}{15}-\frac{15}{12}\right):\left(\frac{11}{20}-\frac{26}{45}\right)\)
\(=\left(\frac{21}{60}+\frac{44}{60}-\frac{75}{60}\right):\left(\frac{99}{180}-\frac{104}{180}\right)\)
\(=-\frac{1}{6}:\frac{-1}{36}\)
\(=\frac{-36}{-6}\)
\(=6\)
ta có công thức \(1.2+2.3+3.4+...+n\left(n+1\right)=\frac{n\left(n+1\right)\left(n+2\right)}{3}\)
áp dụng vào bài ta có \(9.10+10.11+11.12+...+19.20=\frac{19.20.21}{3}-\frac{8.9.10}{3}\)
\(=2660-240\)
\(=2420\)
20 : 11/12
= 20 x 12/11
= 240/11
\(20:\dfrac{11}{12}=20\cdot\dfrac{12}{11}=\dfrac{20\cdot12}{11}=\dfrac{240}{11}\)