Cách làm cho bạn:
Ta có:
- $100a=12,(12)= 12+a$
=> $99a= 100a-a= 12+a -a=12$
=> $a= \frac{12}{99}$
$b=0.1+0.0(21)=\frac{1}{10}+\frac{1}{10}.0,(21)$
Đặt x= 0,(21) thì 100x = 21,(21) = 21 + x
=>x=$\frac{21}{99}$
b= $\frac{1}{10}+\frac{1}{10}.\frac{21}{99}$
=$\frac{1}{10}.1+\frac{21}{99}$
= $\frac{1}{10}.\frac{120}{99}$
= $\frac{12}{99}$
Vậy $a=b$
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