Question

Answer 1

Đổi \(1,2m=120cm\)

Xét ΔOBA và ΔOB'A' có:

\(\widehat{OBA}=\widehat{OB'A'}\left(=90^o\right)\)

\(\widehat{AOB}=\widehat{A'OB'}\left(đ^2\right)\)

\(\Rightarrow\) ΔOBA ∼ ΔOB'A' (g.g)

\(\Rightarrow\dfrac{OB}{OB'}=\dfrac{AB}{A'B'}\left(tsđd\right)\)

\(\Rightarrow\dfrac{OB}{5}=\dfrac{120}{3}\)

\(\Rightarrow3OB=120.5\)

\(\Leftrightarrow3OB=600\)

\(\Leftrightarrow OB=200\left(cm\right)\)

Answer 2

Xét ΔABO và ΔA'B'O ta có:

\(\widehat{ABO}=\widehat{A'B'O}=90^0\)

\(\widehat{AOB}=\widehat{A'OB'}\left(đ.đ\right)\)

→ΔABO ∼ ΔA'B'O(g.g)

\(\rightarrow\dfrac{AB}{A'B'}=\dfrac{BO}{B'O}hay\dfrac{1,2}{3}=\dfrac{BO}{5}\)

\(\Rightarrow BO=\dfrac{1,2.5}{3}=2\left(m\right)\)

Vậy vật AB được đặt cách vật 2 m