Câu 3:
Áp dụng t/c dtsbn:
\(\dfrac{x}{5}=\dfrac{y}{-3}=\dfrac{7x}{35}=\dfrac{2y}{-6}=\dfrac{7x-2y}{35+6}=\dfrac{41}{41}=1\)
\(\Rightarrow\left\{{}\begin{matrix}x=5.1=5\\y=\left(-3\right).1=-3\end{matrix}\right.\)
Câu 4:
a) Ta có: a⊥c,b⊥c
=> a//b
b) Kẻ Cz//a//b
\(\Rightarrow\widehat{BCz}=\widehat{B}=50^0\)
\(\Rightarrow\widehat{ACz}=\widehat{ACB}-\widehat{B}=105^0-50^0=55^0\)
\(\Rightarrow\widehat{A_1}=180^0-\widehat{ACz}=180^0-55^0=125^0\)(trong cùng phía)
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