MQ19---Integration

圖片參考：http://i212.photobucket.com/albums/cc82/doraemonpaul/yahooknowledge/indefiniteintegral/integratecoscosx9.jpg

參考資料：
my wisdom of maths + formula from http://en.wikipedia.org/wiki/List_of_integrals_of_trigonometric_functions#Integrands_involving_only_cosine + http://en.wikipedia.org/wiki/Factorial#Double_factorial + http://mathworld.wolfram.com/DoubleFactorial.html + http://people.math.sfu.ca/~cbm/aands/page_360.htm

Don't trust wolframalpha too much!

e.g.

e^x^2 is integratable, but wolframalpha can't give the ans!

無法以初等函數表示
http://www.wolframalpha.com/input/?i=%E2%88%ABcos%28cosx%29dx