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設長軸為2a,短軸為2b,焦距為2c,則2a+2c=2×2b,即a+c=2b⇒(a+c)2=4b2=4(a2-c2),所以3a2-5c2=2ac,同除a2,整理得5e2+2e-3=0,∴e=35或e=-1(舍去),故選B.
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