Ta có: a//b
=>\(\widehat{A_1}=\widehat{B_3}\)(hai góc so le trong)
mà \(\widehat{A_1}=120^0\)
nên \(\widehat{B_3}=120^0\)
Ta có: \(\widehat{B_3}+\widehat{B_4}=180^0\)(hai góc kề bù)
=>\(\widehat{B_4}+120^0=180^0\)
=>\(\widehat{B_4}=180^0-120^0=60^0\)
Ta có: a//b
=>\(\widehat{D_2}=\widehat{C_4}\)(hai góc so le trong)
mà \(\widehat{D_2}=100^0\)
nên \(\widehat{C_4}=100^0\)
Ta có: \(\widehat{C_2}=\widehat{C_4}\)(hai góc đối đỉnh)
mà \(\widehat{C_4}=100^0\)
nên \(\widehat{C_2}=100^0\)
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