`a)`

`b)`

Xét `ΔOAB` $\backsim$ `ΔOA'B' (g-g)`

`=> (AB)/(A'B') = (OA)/(OA')` hay `3/(h') = 16/(48) => h' = 9cm`

Xét `ΔOIF'` $\backsim$ `ΔA'B'F'`

`=> (OI)/(A'B') = (OF')/(A'F')` mà `OI = A'B'; A'F = OA' - OF'; A'B' = 9cm`

`=> (AB)/(A'B') = (OF')/(OA' - OF')` hay `3/(9) = f/(48-f)`

`=> 48-f = 3f`

`=> f = 12(cm)`

ΔOBA đồng dạng ΔOB'A'

OA/OA'=AB/A'B'

16/48=3/A'B'

A'B'=9CM

ΔOIF' ĐỒNG DANG ΔA'B'F'

OI/A'B'=OF'/A'F'

AB/A'B'=OF'/OA'-OF'

3/9=OF'/48-OF'

OF'=12CM

MÀ OF=OF'=12CM