-20+100:[19-2.(18-21)2]
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\(-20-100:[19-2\left(18-21\right)^2]\)
\(=-20-100:[19-2\left(-3\right)^2]\)
\(=-20-100:[19-2.9]\)
\(=-20-100:\left[19-18\right]\)
\(=-20-100:1\)
\(=-20-100\)
\(=-120\)
-20 - 100 : [19 - 2 (18 - 21)2]
= -20 - 100 : [19 - 2 (-3)2]
= -20 - 100 : (19 - 2 . 9)
= -20 - 100 : (19 - 18)
= -20 - 100 : 1
= -20 - 100
= -120
Có \(\frac{18}{18+19+20}>\frac{18}{18+19+20+21}\)
\(\frac{19}{18+19+21}>\frac{19}{18+19+20+21}\)
\(\frac{20}{18+19+21}>\frac{20}{18+19+20+21}\)
\(\frac{21}{18+19+21}>\frac{21}{18+19+20+21}\)
=> \(\frac{18}{18+19+20}+\frac{19}{18+19+21}+\frac{20}{18+19+21}+\frac{21}{18+19+21}>\frac{18}{18+19+20+21}+\frac{19}{18+19+20+21}+\frac{20}{18+19+20+21}+\frac{21}{18+19+20+21}\)
=> \(\frac{18}{18+19+20}+\frac{19}{18+19+21}+\frac{20}{18+19+21}+\frac{21}{18+19+21}>\frac{18+19+20+21}{18+19+20+21}\)
=>\(\frac{18}{18+19+20}+\frac{19}{18+19+21}+\frac{20}{18+19+21}+\frac{21}{18+19+21}>1\)
=>M>1
Còn lại mình không biết, đúng thì tick nha
\(\dfrac{1}{21}+\dfrac{2}{21}+\dfrac{3}{21}+\dfrac{4}{21}+\dfrac{5}{21}+...+\dfrac{17}{21}+\dfrac{18}{21}+\dfrac{19}{21}+\dfrac{20}{21}\)
\(=\dfrac{1+2+3+4+5+...+17+18+19+20}{21}\)
\(=\dfrac{1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20}{21}\)
\(=\dfrac{210}{21}\)
\(=10\)
2345 - 100 : [19 - 2.(21 - 18)2] = 2345 - 100 : (19 - 2.32)
= 2345 - 100 : (19 - 2.9) = 2345 - 100 : (19 - 18)
= 2345 - 100 = 2245
\(\dfrac{1}{21}+\dfrac{2}{21}+\dfrac{3}{21}+\dfrac{4}{21}+\dfrac{5}{21}+\cdot\cdot\cdot+\dfrac{17}{21}+\dfrac{18}{21}+\dfrac{19}{21}+\dfrac{20}{21}\)
\(=\dfrac{1+2+3+4+5+\cdot\cdot\cdot+17+18+19+20}{21}\)
\(=\dfrac{210}{21}=10\)
-20 + 100 [19 - 2 (18 - 21)2]
= -20 + 100 [19 - 2 (-3)2]
= -20 + 100 (19 - 2 . 9)
= -20 + 100 (19 - 18)
= -20 + 100 . 1 = -20 + 100 = 80
-20+100 : ( 19 -2 . ( 18 -21 )2
= -20 + 100 : ( 19 -2 . ( -3)2 )
= - 20 + 100 : ( 19 -2 . 9 )
= -20 +100 : ( 19 - 18 )
= - 20 + 100 : 1
= -20 +100
= 80