a: Ax\(\perp\)AB
By\(\perp\)AB
Do đó: Ax//By
b: ta có: Ax//By
=>\(\widehat{ACD}+\widehat{CDB}=180^0\)(hai góc trong cùng phía)
=>\(\widehat{CDB}=180^0-130^0=50^0\)
Ta có: \(\widehat{CDB}+\widehat{CDy}=180^0\)(hai góc kề bù)
=>\(\widehat{yDC}+50^0=180^0\)
=>\(\widehat{yDC}=130^0\)
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