题干

如图,△A1B1C1是边长为1的等边三角形,A2为等边△A1B1C1的中心,连接A2B1并延长到点B2,使A2B1=B1B2,以A2B2为边作等边△A2B2C2,A3为等边

△A2B2C2的中心,连接A3B2并延长到点B3,使A3B2=B2B3,以A3B3为边作等边△A3B3C3,依次作下去得到等边△AnBnCn,则等边△A5B5C5的边长为____.


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The Sands of Time

    St Cyrus National Nature Reserve is much more than just golden sands and beautiful flowers. The area has a long human history too. From Stone Age hunters to amazing pioneers, discover the daring deeds and sad stories from St Cyrus' past.

Date: 23rd August 2010

Time. 2 p. m.—3:45 p. m.

Type of event. Guided walk

Between the Tides

    A celebration of the world between the tides. Join local salmon (大马哈鱼) fisherman Jim Ritchie on a fascinating walk to learn how local folk have made a living from the world between the tides, harvesting salmon from the beach at St Cyrus for hundreds of years.

Date: 25th August 2010

Time: 2 p. m.—4 p.m.

Type of event: Family event

Ice & Fire

    St Cyrus National Nature Reserve has had an eventful life! From its days near the equator (赤道) to volcanic eruptions and ice ages. Celebrate the start of Scottish Geology Month with a walk through the reserve and travel back in time to uncover the clues to St Cyrus' past hidden in the cliffs.

Date: 31st August 2010

Time: 2 p. m.—3:45 p. m.

Type of event: Guided walk

Scary Stories

    It's getting darker at nights... it's almost Halloween, when the ghosts (鬼怪) come out to play. Join us for some spooky stories of Dinnet and Deeside long ago... and listen out for things that sound strange in the night!

Date: 25th October 2010

Time: 7 p. m.—9 p. m.

Type of event: Family event

Note:

* All under 18's must be accompanied by an adult

* Pets allowed: No

* Cost: Free

* Phone: 01674­830736

* Location: SNH Visitor Centre, St Cyrus National Nature Reserve