< 2 = 180° - < 1 =100° ;
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2)
2*-------
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3) <2 - <1 =20° ;<br>-----------------
<2 ==>? ; <1 ==>?
<2 +<1 =180° (вертикальные углы);<br>{ <2 - <1 =20° ;<2 +<1 =180°.<br>(<2 - <1)+(<2 +<1) =20°+180°;<br>2 *<2 =200°;<br><2 =100° .<br><1 =180° - 100° =80° . *** или <1 =<2 -20° =100° -20° =80° ***