x + 123 = 985
x - 124 = 857
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Phep so sanh nao dung?
A. 123/124 > 124/125
B. 123/124=124/125
C. 123/124<124/125
D. 123/124 = 124-1/125
Ta có :
\(121.124=\left(123-2\right)\left(123+2\right)=123^2-2^2< 123^2\)
\(\Rightarrow A< B\)
\(123\times35+124\times65\)
\(=123\times35+\left(123+1\right)\times65\)
\(=123\times35+123\times65+65\)
\(=123\times\left(35+65\right)+65\)
\(=123\times100+65\)
\(=12300+65\)
\(=12365\)
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
\(\dfrac{x+1}{124}+1+\dfrac{x+2}{123}+1=\dfrac{x+3}{122}+1+\dfrac{x+4}{121}+1\)
\(\Leftrightarrow\dfrac{x+125}{124}+\dfrac{x+125}{123}=\dfrac{x+125}{122}+\dfrac{x+125}{121}\)
\(\Leftrightarrow\left(x+125\right)\left(\dfrac{1}{124}+\dfrac{1}{123}-\dfrac{1}{122}-\dfrac{1}{121}\ne0\right)=0\Leftrightarrow x=-125\)
<=>\(\dfrac{x+1}{124}+\dfrac{x+2}{123}-\dfrac{x+3}{122}-\dfrac{x+4}{121}=0\)
<=>\(\left(\dfrac{x+1}{124}+1\right)+\left(\dfrac{x+2}{123}+1\right)-\left(\dfrac{x+3}{122}+1\right)-\left(\dfrac{x+4}{121}+1\right)=0\)
<=>\(\dfrac{x+125}{124}+\dfrac{x+125}{123}-\dfrac{x+125}{122}-\dfrac{x+125}{121}=0\)
<=>\(\left(x+125\right)\left(\dfrac{1}{124}+\dfrac{1}{123}-\dfrac{1}{122}-\dfrac{1}{121}\right)=0\)
<=>x+125=0
<=>x=-125
x + 123 = 985
x = 985 - 123
x = 862
x - 124 = 857
x = 857 + 124
x = 981
x+123=985 =>x=985-123 =>x=862
x-124=857 =>x=857+124 =>x=981