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`#Sky`

`"Câu 2:"`

`a)S`

`b)Đ`

`c)Đ`

`d)S`

________________________

Giải thích:

Ta có: `a=51+-1 cm`

`=>\overline{a}=51 (cm) , \Deltaa=1 (cm)`

Ta có: `b=49+-1 cm`

`=>\overline{b}=49 (cm) , \Deltab=1 (cm)`

`a)` `F=a+b`

`\DeltaF=\Deltaa+\Deltab=1+1=2 (cm)`

`\overline{F}=\overline{a}+\overline{b}=51+49=100 (cm)`

`\deltaF=(\DeltaF)/({F}). 100%=2%`

`-> A` sai

`b)` `F=a-b`

`\DeltaF=\Deltaa+\Deltab=1+1=2 (cm)`

`\overline{F}=\overline{a}-\overline{b}=51-49=2 (cm)`

`\deltaF=(\DeltaF)/({F}). 100%=100%`

`->B` đúng

`c) F=a.b`

`\deltaa=(\Deltaa)/(\overline{a}).100%=1/(51). 100%`

`\deltab=(\Deltab)/(\overline{b}).100%=1/(49). 100%`

`\deltaF=\deltaa+\deltab=4%`

`->C` đúng

`d)`

`F=a/b`

`\deltaa=(\Deltaa)/(\overline{a}).100%=1/(51). 100%`

`\deltab=(\Deltab)/(\overline{b}).100%=1/(49). 100%`

`\deltaF=\deltaa+\deltab=4%`

`->D` sai