Đáp án:
Bạn tham khảo nhé!
Giải thích các bước giải:
$-5,12=\dfrac{-512}{100}=\dfrac{-128}{25}$
$A=0,(72)=0,727272...\\\Rightarrow 1000A=727,27272...\\\Rightarrow 10A=7,27272...\\\Rightarrow 1000A-10A=727,27272...-7,27272...\\\Rightarrow 990A=720\\\Rightarrow A=\dfrac{8}{11}$
Vậy $0,(72)=\dfrac{8}{11}$.
$A=0,2(36)=0,2363636...\\\Rightarrow 1000A=236,363636...\\\Rightarrow 10A=2,363636...\\\Rightarrow 1000A-10A=236,363636...-2,363636...\\\Rightarrow 990A=234\\\Rightarrow A=\dfrac{13}{55}$
Vậy $0,2(36)=\dfrac{13}{55}$.
$A=3,(234)=3,234234...\\\Rightarrow 1000A=3234,234234...\\\Rightarrow 1000A-A=3234,234234...-3,234234...\\\Rightarrow 999A=3231\\\Rightarrow A=\dfrac{359}{111}$
Vậy $0,2(36)=\dfrac{359}{111}$.
$A=2,71(3)=2,713333...\\\Rightarrow 1000A=2713,3333...\\\Rightarrow100A=271,3333...\\\Rightarrow 1000A-100A=2713,3333...-271,3333...\\\Rightarrow 900A=2442\\\Rightarrow A=\dfrac{407}{150}$
Vậy $2,71(3)=\dfrac{407}{150}$.
$A=7,12(54)=7,125454...\\\Rightarrow 10000A=71254,5454...\\\Rightarrow 100A=712,5454...\\\Rightarrow 10000A-100A=71254,5454...-712,5454...\\\Rightarrow 990A=70542\\\Rightarrow A=\dfrac{3919}{550}$
Vậy $2,71(3)=\dfrac{3919}{550}$.
