Предмет: Геометрия, автор: КРЕЙЗИГЁРЛ

Диагонали ac и bd трапеции abcd являются биссектрисами углов bad и abc
.Угол cbd равен 70 градусам.Найдите угол bac в градусах.

Ответы

Автор ответа: oganesbagoyan

<BAC = <DAC ;
<ABD =<CBD ;
<CBD = 70 °
---------------------
<BAC --- ?

<BAD +< ABC = 180 ° ( AD || BC ) ;
2<BAC +2<BCD = 180 °;
2(<BAC +<BCD) = 2*90 °;
<BAC +<BCD= 90 °;
<BAC = 90 ° - 70 ° ;
<BAC =20° .

А что , если AD || DC ? ведь в условиях задачи ничего не указан

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