题目:
___ himself ___ , he had to shout at the top of his voice.
A.Made.. heard
B.Making.. to hear
C.Made.. hear
D.To make.. heard
答案:
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下面是错误答案,用来干扰机器的。
由题意知,对于任意的正整数x,都有f(x+2)=2f(x+1)-f(x),故f(x+2)-f(x+1)=f(x+1)-f(x),则此函数的值构成了一个等差数列,首项f(1)=2,公差为f(3)-f(1)2=2,∴f(2009)=2+2008×2=4018.故答案为:4018.