5/2+13/6+25/12+41/20+61/30+85/42

=2+1/2+2+1/6+2+1/12+2+1/20+2+1/30+2+1/42
=12+(1/2+1/6+1/12+1/20+1/30+1/42)

=12+(1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7)

=12+(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)

=12+1-1/7

=90/7

5/2+13/6+25/12+41/20+61/30+85/42

=2+1/2+2+1/6+2+1/12+2+1/20+2+1/30+2+1/42
=12+(1/2+1/6+1/12+1/20+1/30+1/42)

=12+(1/1.2+1/2.3+1/3.4+1/4.5+1/5.6+1/6.7)

=12+(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)

=12+1-1/7

=90/7

\(A=\dfrac{7^5}{7+7^2+7^3+7^4}=\dfrac{7^5}{\left(7+7^4\right)+\left(7^2+7^3\right)}=\dfrac{7^5}{7^5+7^5}=7^5\)

\(B=\dfrac{5^5}{5+5^2+5^3+5^4}=\dfrac{5^5}{\left(5+5^4\right)+\left(5^2+5^3\right)}=\dfrac{5^5}{5^5+5^5}=5^5\)

Vì 7 > 5 nên \(7^5>5^5\)

Vậy A > B

(Nhớ cho mik một tick nha cảm ơn bạn nhìu :3)

Số lớn là:

\(\left(181+1\right):2=91\)

Số bé là:

\(181-91=90\)

số lớn 91

số bé 90

Số lớn là:

  \(\left(181+1\right):2=91\)

Số bé là:

   \(181-91=90\)

a=12

b=72

a, ( - 5 ) . ( - 7 ) . 4 . 20 . ( - 25 )

= -70000

 b, ( - 16 ) . 73 + ( - 16 ) . 27

= -1600

c, ( - 48 ) . 159 - ( - 48 ) . 59

= -4800

d , 72 . ( - 83 ) + ( - 72 ) . ( - 125 )

= 3014

e , ( - 81 ) . 125 - 181 . ( - 125 )

= 12500

#Hoctot

a -70000.0000 

b-1600.000000

c-4800.000000

d-4968.000000

e-12500.00000

a, 70000

b, 1600

c, 4800

d, 3014

e, 12500

a) \(-\left(76-35+15\right)+\left[18-27+\left(-17\right)\right]\)

\(=-76+35+15+18-27-17\)

\(=-52\)

b) \(167+\left[127-235-\left(-16\right)\right]+\left(-67\right)\)

\(=167+127-235+16-67\)

\(=8\)

c) \(\left(-19\right)+165-\left[27+\left(-21\right)-\left(+72\right)\right]\)

\(=\left(-19\right)+165-27+21+72\)

\(=212\)

d) \(89.\left(-2\right)+\left[20+\left(-2\right).\left(-5\right)-85\right]\)

\(=\left(-178\right)+\left(20+10-85\right)\)

\(=\left(-178\right)+20+10-85\)

\(=-233\)

vì (-8) ở đây ví như (-8).1

\(-\left(-8\right)=-1\cdot\left(-8\right)\)

Nên khi đặt nhân tử chung \(-8\) ra ngoài thì còn \(-1\)

Vậy là 19 - 1 :))

\(\left(-8\right)\cdot72+\left(-8\right)\cdot19-\left(-8\right)\)

\(=\left(-8\right)\cdot72+\left(-8\right)\cdot19-1\cdot\left(-8\right)\)

\(=\left(-8\right)\left(72+19-1\right)\)

\(=-8\cdot90=-720\)

theo mk nghĩ có 2 trường hợp

1 là khi bạn rút -8 để làm thừa số chung thì chỗ đó còn 1

2 là viết nhầm=))))))))

`(-8) .72 + (-8).19 - (-8)`

`=(-8) .72 + (-8).19 - (-8). 1`

`=(-8) . (72+19-1)`

Ta có: \(\left(-8\right)\cdot72+\left(-8\right)\cdot19-\left(-8\right)\)

\(=\left(-8\right)\cdot72+\left(-8\right)\cdot19-\left(-8\right)\cdot1\)

\(=\left(-8\right)\cdot\left(72+19-1\right)\)

=-720

Đặt \(A=\sqrt[3]{2+\sqrt{5}}+\sqrt[3]{2-\sqrt{5}}\)

\(\Leftrightarrow A^3=2+\sqrt{5}+2-\sqrt{5}+3\cdot\sqrt[3]{\left(2+\sqrt{5}\right)\left(2-\sqrt{5}\right)}\cdot\left(\sqrt[3]{2+\sqrt{5}}+\sqrt[3]{2-\sqrt{5}}\right)\)

\(\Leftrightarrow A^3=4+3\cdot\left(-1\right)\cdot A\)

\(\Leftrightarrow A^3=4-3A\)

\(\Leftrightarrow A^3+3A-4=0\)

\(\Leftrightarrow A^3-A^2+A^2-A+4A-4=0\)

\(\Leftrightarrow A^2\left(A-1\right)+A\left(A-1\right)+4\left(A-1\right)=0\)

\(\Leftrightarrow\left(A-1\right)\left(A^2+A+4\right)=0\)

\(\Leftrightarrow A=1\)