Vì x//y
nên: $\widehat{B}$$_{2}=$ $\widehat{C}$$_{2}$ ( 2 góc so le trong) $\Rightarrow$$\widehat{C}$$_{2}=$ $\widehat{B}$$_{2}=$ $70^\circ$
Ta có: $\widehat{C}$$_{2}$ $+$ $\widehat{C}$$_{4}$ $=180^\circ$( 2 góc kề bù) $\Rightarrow$$\widehat{C}$$_{4}=$ $180^\circ-$ $\widehat{C}$$_{2}$ $\Rightarrow$$\widehat{C}$$_{4}=$ $180^\circ-$ $70^\circ$ $=110^\circ$
Ta lại có: $\widehat{B}$$_{2}$ $+$ $\widehat{B}$$_{4}$ $=180^\circ$( 2 góc kề bù) $\Rightarrow$$\widehat{B}$$_{4}=$ $180^\circ-$ $\widehat{B}$$_{2}$ $\Rightarrow$$\widehat{B}$$_{4}=$ $180^\circ-$ $70^\circ$ $=110^\circ$
