共50条信息
设平面\(\alpha{/\!/}\)平面\(\beta{,}A{,}C{∈}\alpha{,}B{,}D{∈}\beta\),直线\(AB\)与\(CD\)交于点\(S\),且点\(S\)位于平面\(\alpha{,}\beta\)之间,\({AS}{=}8{,}{BS}{=}6{,}{CS}{=}12\),则\({SD}{=}\) ______ .
选修\(4-1\):几何证明选讲
如图,\(∆ABC \)的角平分线\(AD \)的延长线交它的外接圆于点\(E \).
\((\)Ⅰ\()\)证明:\( \dfrac{AB}{AE}= \dfrac{AD}{AC} \);
\((\)Ⅱ\()\)若\(∆ABC \)的面积\(S= \dfrac{1}{2}AD·AE \),求\(∠BAC \)的大小.
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