C6 $\widehat{A}=\widehat{D}=70^o$
Mà $\widehat{A}, \widehat{D}$ so le trong
$⇒AB//CD$
$⇒\widehat{B}=\widehat{C_1}=40^o$ (So le trong)
$\widehat{C_1}+\widehat{C_2}=180^o$ (Kề bù)
$⇒\widehat{C_2}=180^o-\widehat{C1}=180^o-40^o=140^o$
C7 $IH⊥IE, IE⊥EG$
$⇒IH//EG$
$⇒\widehat{H_1}=\widehat{G}=135^o$ (So le trong)
$\widehat{H_2}+\widehat{H_1}=180^o$ (Kề bù)
$⇒\widehat{H_2}=180^o-\widehat{H_1}=180^o-135^o=45^o$
$⇒\widehat{H_2}=\widehat{H_3}=45^o$ (Đối đỉnh)
