Ta có: \(\widehat{A}+\widehat{B}+\widehat{C}=180^o\)
mà \(\widehat{B}+\widehat{C}=90^o\)
Do đó: \(\widehat{A}=90^o\)
\(\Rightarrow AB\perp AC\) \(\left(đpcm\right)\)
Hình vẽ:
Giải:
Ta có: \(\widehat{ABC}+\widehat{ACB}=90^0\)
Hay \(\widehat{B}+\widehat{C}=90^0\)
Vì \(\widehat{A}+\widehat{B}+\widehat{C}=180^0\)
Mà \(\widehat{B}+\widehat{C}=90^0\)
Nên \(\widehat{A}+\widehat{B}+\widehat{C}=\widehat{A}+90^0=180^0\)
\(\Leftrightarrow\widehat{A}=180^0-90^0=90^0\)
\(\Leftrightarrow\Delta ABC\) vuông tại A
\(\Leftrightarrow AB\perp AC\)
\(\Rightarrowđpcm\).
Chúc bạn học tốt!!!
