a(n+1) ^2=4an
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anâ¥0
a1=1>0ï¼å设å½n=k(kâN+)æ¶ï¼ak>0ï¼åå½n=k+1æ¶
a(k+1) ^2=4ak >0
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a(n+1)^2=4an
log4[a(n+1)^2]=log4(4an)
2log4 [a(n+1)]=log4 (an) +1
2log4[a(n+1)] -2=log4(an) -1
2[log4(a(n+1) -1]=log4(an) -1
[log4(a(n+1) -1]/[log4(an) -1]=1/2ï¼ä¸ºå®å¼
log4(a1) -1=log4(1) -1=0-1=-1
æ°å{log4(an) -1}æ¯ä»¥-1为é¦é¡¹ï¼1/2为å
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log4(an) -1=(-1)Ã(1/2)^(n-1)
log4(an) =1 - 1/2^(n-1)
an=4^[1- 1/2^(n-1)]
æ°å{an}çé项å
¬å¼ä¸ºan=4^[1- 1/2^(n-1)]
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