已知a为锐角,且tana=根号2-1,函数f(x)=2x.tan2a+sin(2a+派/4),数列{An}的首项a1=1 An+1=f(an) 求函数f(x)的表达式
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答：只要求f(x)表达式吗?
锐角a满足：tana=√2-1>0tan(2a)=2tana /(1-tan²a)
=2(√2-1) /[1-(√2-1)²]
=2(√2-1)/(2√2-2)
=1所以：2a=π/4,a=π/8
f(x)=2xtan(2a)+sin(2a+π/4)
=2x+sin(π/4+π/4)
=2x+1所以：f(x)=2x+1
An数列首项A1=1
A(n+1)=f(An)=2An +1
A(n+1)-An=An +1