Trả lời :

Phép so sánh C đúng nhoa bn =))

~ Thiên Mã ~

Đáp án đúng là câu C

A = 123 . 123

A = 15129.

B = 121 . 124

B = 15004.

=> 15129 >15004.

Vậy: A > B.

Ta có :

\(121.124=\left(123-2\right)\left(123+2\right)=123^2-2^2< 123^2\)

\(\Rightarrow A< B\)

Đoan cuối là A>B nhs

123/124<124/125

123/124>123/125

12365

123 x 35 + 124 x 65

= 4305 + 8060

= 12365

\(123\times35+124\times65\)

\(=123\times35+\left(123+1\right)\times65\)

\(=123\times35+123\times65+65\)

\(=123\times\left(35+65\right)+65\)

\(=123\times100+65\)

\(=12300+65\)

\(=12365\)

123 x 35 + 124 x 65

= 123 x 35 + 123 x 65 + 65

= 123 x (35 + 65) + 65

= 123 x 100 + 65

= 12300 + 65

= 12365

=4305+8060

=12365

=12365

123 x 35 + 124 x 65 

= 4305 + 8060

=12365

12365

\(\dfrac{x+1}{124}+1+\dfrac{x+2}{123}+1=\dfrac{x+3}{122}+1+\dfrac{x+4}{121}+1\)

\(\Leftrightarrow\dfrac{x+125}{124}+\dfrac{x+125}{123}=\dfrac{x+125}{122}+\dfrac{x+125}{121}\)

\(\Leftrightarrow\left(x+125\right)\left(\dfrac{1}{124}+\dfrac{1}{123}-\dfrac{1}{122}-\dfrac{1}{121}\ne0\right)=0\Leftrightarrow x=-125\)

<=>\(\dfrac{x+1}{124}+\dfrac{x+2}{123}-\dfrac{x+3}{122}-\dfrac{x+4}{121}=0\)

<=>\(\left(\dfrac{x+1}{124}+1\right)+\left(\dfrac{x+2}{123}+1\right)-\left(\dfrac{x+3}{122}+1\right)-\left(\dfrac{x+4}{121}+1\right)=0\)

<=>\(\dfrac{x+125}{124}+\dfrac{x+125}{123}-\dfrac{x+125}{122}-\dfrac{x+125}{121}=0\)

<=>\(\left(x+125\right)\left(\dfrac{1}{124}+\dfrac{1}{123}-\dfrac{1}{122}-\dfrac{1}{121}\right)=0\)

<=>x+125=0

<=>x=-125