Mình cũng chịu thôi

A=1,05+0,23+4,61+a,b0c  A=5,79+a,b0c 

B=5,59+0,02+a,b0c   B=5,61+a,b0c

Vậy A>B

a)A=1+0,b+0,05+a+0,23+4+0,61+0,00c=5+a,b0c+0,89=5,89+a,b0c

  B=a+0,b+0,00c+0,02+5,59=a,b0c+5,61

Vậy A>B.

b)A=a+0,0c+0,b+0,2+7,05=a,bc+7,07

  B=a,bc+7,25

Vậy A<B

Ta có : \(\dfrac{1}{2}< \dfrac{1}{1.2};\dfrac{1}{2^2}< \dfrac{1}{2.3};...;\dfrac{1}{2^{10}}< \dfrac{1}{9.10}\)

\(\Rightarrow\dfrac{1}{2}+\dfrac{1}{2^2}+...+\dfrac{1}{2^{10}}< \dfrac{1}{1.2}+\dfrac{1}{2.3}+...+\dfrac{1}{9.10}\)

\(=1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{9}-\dfrac{1}{10}=\dfrac{9}{10}< 1\Rightarrow A< B\)

Lời giải:
a.

\(\overline{a,87}+\overline{2,b2}=a+0,87+2,02+\overline{0,b}\\ =(a+\overline{0,b})+(0,87+2,02)\\ =\overline{a,b}+2,89\)

b.

\(\overline{3a,81}+\overline{4,b5}+\overline{13,9c}=30,81+a+4,05+\overline{0,b}+13,9+\overline{0,0c}\\ =(30,81+4,05+13,9)+(a+\overline{0,b}+\overline{0,0c})\\ =48,76+\overline{a,bc}=\overline{a,bc}+20,36+28,4> \overline{a,bc}+20,36+28,04 \)

P/s : mk làm phần b trước

\(6\cdot5^{22}=\left(5+1\right)\cdot5^{22}=5^{23}+5^{22}>5^{23}\)

Hok tốt

a) đây :

\(72^{45}-72^{44}=72^{44}\cdot72-72^{44}=72^{44}\cdot\left(72-1\right)\)

\(72^{44}-72^{43}=72^{43}\cdot72-72^{43}=72^{43}\cdot\left(72-1\right)\)

mà \(72^{44}>72^{43}\)=> \(72^{44}\cdot\left(72-1\right)>72^{43}\cdot\left(72-1\right)\)

=> \(72^{45}-72^{44}>72^{44}-72^{43}\)

Lời giải:

$B=\overline{4a,86}+\overline{8,b5}+\overline{18,9c}$

$=40,86+a+8,05+0,b+18,9+0,0c$

$=(40,86+8,05+18,9)+(a+0,b+0,0c)$

$=67,81+\overline{a,bc}< 68,5+\overline{a,bc}$

Vậy $B< A$

ta có x^100> 0

=> x>0 

mà x^100=x

suy ra x^99=1  ( chia cả 2 vế cho x )

=> x=1

a, \(\overline{a,87}\) + \(\overline{2,b2}\)

 = \(\overline{a,0}\) + 0,87 + 2,02 + \(\overline{0,b}\) 

= \(\overline{a,b}\) + 2,89 

vì 2,89 > 2,86 vậy \(\overline{a,87}\) + \(\overline{2,b2}\)  > \(\overline{a,b}\) + 2,86 

b, \(\overline{a,bc}\) + 20,04+ 28,63 

= \(\overline{a,bc}\) + 48,67

= 48,67 + \(\overline{a,b}\) + \(\overline{0,0c}\)

=\(\overline{48,67c}\) + \(\overline{a,b}\)

\(\overline{3a,81}\) + \(\overline{4,b5}\) + 13,9

= 30,81 + \(\overline{a,0}\) + 4,05 + 13,9 + \(\overline{0,b}\)

= 48,76 + \(\overline{a,b}\)

Vì 48,76 > \(\overline{48,67c}\)

Nên \(\overline{3a,81}\) + \(\overline{4,b5}\) + 13,9 > \(\overline{a,bc}\) + 20,04 + 28,63

Lời giải:

a.
\(\overline{a,8b}+\overline{2,b2}=\overline{a,0b}+0,8+2,02+\overline{0,b}=2,82+\overline{a,bb}\)

Không có cơ sở để so sánh với $\overline{a,b}+2,86$ bạn nhé.

b.

\(\overline{3a,81}+\overline{4,b5}+\overline{13,9c}=30,81+a+4,05+\overline{0,b}+13,9+\overline{0,0c}\)

$=30,81+4,05+13,9+a+\overline{0,b}+\overline{0,0c}$

$=48,76+\overline{a,bc}$

$\overline{a,bc}+20,04+28,63=\overline{a,bc}=48,67$

Suy ra $\overline{a,bc}+20,04+28,63< \overline{3a,81}+\overline{4,b5}+\overline{13,9c}$

giúp với