Question

Answer 1

a) Xét \(\Delta ABC:\)

\(AB^{\text{2}}=\text{2}5^{\text{2}}=6\text{2}5.\)

\(BC^{\text{2}}+CA^{\text{2}}=7^{\text{2}}+\text{2}4^{\text{2}}=6\text{2}5.\)

\(\Rightarrow AB^{\text{2}}=BC^{\text{2}}+CA^{\text{2}}.\)

\(\Rightarrow\Delta ABC\) vuông tại C (Định lý Pytago đảo).

b) Xét \(\Delta DEF:\)

\(FD^{\text{2}}=\sqrt{15}^{\text{2}}=15.\)

\(DE^{\text{2}}+EF^{\text{2}}=2^{\text{2}}+\sqrt{11}^{\text{2}}=11\text{1}5.\)

\(\Rightarrow FD^{\text{2}}=DE^{\text{2}}+EF^{\text{2}}.\)

\(\Rightarrow\) \(\Delta DEF\) vuông tại E (Định lý Pytago đảo).