填充第10題:
小弟用土法煉鋼,先利用規律做出\(f\left( f\left( f\left( x \right) \right) \right)\)的圖形:
先觀察到\(f\left( \left[ 0,1 \right] \right)=\left[ 0,1 \right]\), 然後求出函數圖形的折點在於絕對值內部為0之處,即\(f\left( x \right)=0\), \(f\left( f\left( x \right) \right)=0\), \(f\left( f\left( f\left( x \right) \right) \right)=0\)之處,求出折點為\(x=\frac{1}{8},\frac{2}{8},\ldots ,\frac{7}{8}\)共7個,加上定義域端點\(x=0,1\) 後用直線連接得到\(f\left( f\left( f\left( x \right) \right) \right)\)在\([0,1]\)的圖形為4個V字形(抱歉我沒有用圖,各位可畫畫看),故所求答案為8個解。
故本題為函數圖形的迭代,f(x)的圖形在[0,1]為1個V字,f(f(x))的圖形在[0,1]為2個V字,f(f(f(x)))的圖形在[0,1]為4個V字,.....
迭代n次的函數\({{f}^{(n)}}\left( x \right)\) 在[0,1]為\({{2}^{n-1}}\)個V字(連續排列),故此時交點個數為\({{2}^{n}}\)個
Let \( f(x)= |2\{x\}-1| \) where \( \{x\} \) denotes the fractional part of \( x \) . The number \( n \) is the smallest pohsitive integer such that the equation
\( nf(xf(x)) = 2012 \) has at least 2012 real solutions \( x \). What is \( n \) ?
Note: the fractional part of \( x \) is a real number \( y = \{x\} \) , such that \( 0 \leq y <1 \) and \( x - y \) is an integer. 作者: 阿光 時間: 2014-6-10 15:38