先化簡，再求值：
．其中
滿足一元二次方程
．
解：
=
······························································································· 2分
=
··························································································· 3分
=
=
．··············································································································· 5分
化簡方程 得：
，··················································································································· 6分
解得
，
．·········································································································· 8分
因為當時原式無意義，所以舍去； ··············································································· 9分
當時，原式=
．··························································································· 10分
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，則底角為 ．
B．
C．
D．
，則這個正六邊形的面積為 cm2．
=﹣3