数列 (16 0:36:31)设数列f(x)=1/2^x+根号2,求f(-5)+f(-4)+...+f(0)+...+f(6)的值
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数列 (16 0:36:31)设数列f(x)=1/2^x+根号2,求f(-5)+f(-4)+...+f(0)+...+f(6)的值
数列 (16 0:36:31)
设数列f(x)=1/2^x+根号2,求f(-5)+f(-4)+...+f(0)+...+f(6)的值
数列 (16 0:36:31)设数列f(x)=1/2^x+根号2,求f(-5)+f(-4)+...+f(0)+...+f(6)的值
求 f(x) + f(1-x)
f(x) = 1/(2^x + √2)
f(1-x)
= 1/[2^(1-x) + √2) .(分子、分母同时乘以 2^x )
= 2^x/(2 + √2 * 2^x) .(分母中提取出 √2)
= (2^x/√2) * (1/√2 + 2^x)
= (2^x/√2) * f(x)
f(x) + f(1-x)
= (1+ 2^x/√2) * f(x)
=[ (√2 + 2^x)/√2 ] * f(x)
= [1/√2*f(x)] * f(x)
= 1/√2
f(-5)+f(-4)+…+f(0)+…+f(5)+f(6)
= [f(-5) + f(6)] + [f(-4) + f(5)] + [f(-3) + f(4)] + [f(-2) + f(3)] + [f(-1) + f(2)] + [f(0) + f(1)]
= 6/√2
=3√2
原试=1/2^(-5)+1/2^(-4)+...+1/2^(0)+...+1/2^(6)+6*根号2
(注解:这等于是合并同类项)
=2^(6)-1/2^(-5)+6*根号2
(注解:2^(6)-1/2^(-5)是用等比数列前N项和公式算出来的)