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84:4+3^9 : 3^7 + 5^0
= 84:4 + 3^2 +1
=84:4+9+1
=21+9+1
=30+1
=31
Mk làm đúng thì k và kb nha , Poi
2:
a: =4+3/8+5+2/3
=9+3/8+2/3
=216/24+9/24+16/24
=216/24+25/24
=241/24
b; =2+3/8+1+1/4+3+6/7
=6+3/8+1/4+6/7
=6+5/8+6/7
=419/56
c: \(=2+\dfrac{3}{8}-1-\dfrac{1}{4}+5+\dfrac{1}{3}\)
=6+3/8-1/4+1/3
=6+1/8+1/3
=6+11/24
=155/24
d: \(=3+\dfrac{5}{6}+6\cdot\dfrac{13}{6}\)
=3+13+5/6
=16+5/6
=101/6
e: =3+1/2+4+5/7-5-5/14
=3+4-5+1/2+5/7-5/14
=2+7/14+10/14-5/14
=2+12/14
=2+6/7=20/7
f: =9/2+1/2:11/2
=9/2+1/11
=99/22+2/22=101/22
84 : 4 + 39 : 37 + 5
= 21 + 39 - 7 + 5
= \(21 +3^{2} + 5\)
= \(21 +9 + 5\)
= 35
-84 : 4 + 39 : 37 + 50
= -21 + 32 + 1
= -21 + 9 + 1
= -21 + 10
= -11
Đáp số : -11
Áp dụng tc: \(\frac{1}{n}.\left(1+2+3+...+n\right)=\frac{1}{n}.\frac{n.\left(n+1\right)}{2}=\frac{n+1}{2}\)
=> H = \(\frac{1}{2}.2+\frac{1}{2}.3+\frac{1}{2}.4+...+\frac{1}{2}.85=\frac{1}{2}.\left(2+3+4+...+85\right)\)
= \(\frac{1}{2}.\left(1+2+3+4+...+85-1\right)=\frac{1}{2}.\left(\frac{85.86}{2}-1\right)=\frac{1}{2}.3654=1827\)
e)5/9:5/3=5/9.5/3
=25/27
g)0:-/11=0
Vi 0 chia cho bat ki so nao cung bang 0
Bài 1:
a) \(\dfrac{65}{91}+\dfrac{-33}{55}=\dfrac{5}{7}+\dfrac{-3}{5}=\dfrac{25}{35}+\dfrac{-21}{35}=\dfrac{4}{35}\)
b) \(\dfrac{36}{-84}+\dfrac{100}{450}=\dfrac{-3}{7}+\dfrac{2}{9}=\dfrac{-27}{63}+\dfrac{14}{63}=\dfrac{-13}{63}\)
\(84:4+3^9:3^7+5^0\)
\(=84:4+3^{9-7}+1\)
\(=84:4+3^2+1\)
\(=84:4+9+1\)
\(=21+9+1\)
\(=30+1\)
\(=31\)