一條超難數學題!!!!!!!!!!!!
回答 (7)
2007-04-22 12:00 am
By " 旋轉 ", it should be taken to mean a complete revolution, i.e. a turn of 360 degrees. Therefore, after 2 revolutions (or " n " revolutions so long as n is a positive integer), P should remain in its original position and hence the answer is A.
There is nothing to do with whether PQRS is a triangular pyramid or the relative position of where the line AB cuts the plane PQR.
There is nothing to do with whether PQRS is a triangular pyramid or the relative position of where the line AB cuts the plane PQR.
2007-04-21 6:59 am
Assume the rotation is completely,
Let the incentre of triangle PQR be O,
Let the length of each side = a
in triangle PQR,
O is the center of the inscribed circle of triangle PQR,
extend PO to QR and the interception of them is M,
OM perpendicular to RQ ( tanger perp. radius)
RM = MQ (prop. of isos. triangle)
thus, O is also the centroid of the inscribed circle of triangle PQR,
the projection of S on plane PQR is O
SO perpendicular to plane PQR
thus, after two complete rotation, the new position is P
Let the incentre of triangle PQR be O,
Let the length of each side = a
in triangle PQR,
O is the center of the inscribed circle of triangle PQR,
extend PO to QR and the interception of them is M,
OM perpendicular to RQ ( tanger perp. radius)
RM = MQ (prop. of isos. triangle)
thus, O is also the centroid of the inscribed circle of triangle PQR,
the projection of S on plane PQR is O
SO perpendicular to plane PQR
thus, after two complete rotation, the new position is P
參考: Keith ^^
2007-04-21 12:53 am
i think is Q
2007-04-21 12:52 am
何謂「兩次旋轉」呢？數學不是文學，要講得清清楚楚才可以的
2007-04-20 10:42 pm
C)R
因為佢係一個正４面體, 所有面都係一樣
而S係 三角形PQR o既中心點
so 第一次轉, P會去左Q, Q會去左R then R會去左P
第二次轉 P會去左R 所以答案應該係 R
因為佢係一個正４面體, 所有面都係一樣
而S係 三角形PQR o既中心點
so 第一次轉, P會去左Q, Q會去左R then R會去左P
第二次轉 P會去左R 所以答案應該係 R
參考: me
2007-04-20 10:27 pm
我認為, 應該是P.............
收錄日期: 2021-04-12 23:07:24
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070420000051KK01567