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標題:

Geometry. Find the angle.

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圖片參考：http://imgcld.yimg.com/8/n/HA04776011/o/701012190089413873429330.jpg Square ABCD is rotated through 15 degree anticlockwise about A to AB'C'D'. Find∠CC'B'.

最佳解答:

∠CAB=45 (diagonal of square) ∠C'AB=45+15=60 (C is rotated 15 about A) Consider the triangle ACC', ∠C'AC=∠C'AB-∠CAB=60-45=15 triangle ACC' is isoceles (since AC=AC') ∠C'CA=(180-∠C'AC)/2=(180-15)/2=82.5(∠ sum of triangle) ∠CC'B=∠C'CA+∠ACB=82.5+45=127.5 2010-12-19 19:51:01 補充： sorry... ∠CC'B' =∠CC'A-∠AC'B' =82.5-45 =37.5 I have calculated ∠C'CB..

其他解答:

∠CC'B = ∠C'CA - ∠ACB