Câu 1:
- 1 cặp góc so le trong: \(\widehat{A_4}=\widehat{B_2}.\)
- 1 cặp góc đồng vị: \(\widehat{A_3}=\widehat{B_3}.\)
- 1 cặp góc trong cùng phía: \(\widehat{A_1};\widehat{B_2}\)
Câu 2:
a) Ta có: a // b (gt).
a \(\perp\) c (gt).
\(\rightarrow\) b \(\perp\) c.
b) b \(\perp\) c (cmt). \(\rightarrow\) \(\widehat{B}=90^o.\)
a // b (gt). \(\rightarrow\) \(\widehat{D}=\widehat{C}\) (so le trong).
Mà \(\widehat{C}=115^o.\)
\(\rightarrow\widehat{D}=115^o.\)
Câu 3:
Xét tam giác ABC:
\(\widehat{BAC}+\widehat{B}+\widehat{C}=180^o\) (Tổng 3 góc trong tam giác).
\(\rightarrow80^o+x+40^o=180^o.\rightarrow x=60^o.\)
Ta có: \(y+\widehat{BAC}=180^o\) (2 góc kề bù).
\(\rightarrow y+80^o=180^o.\rightarrow y=100^o.\)
