什么是f(x)= 4x ^ 2-2x + x /(x-1/4)的局部极值?

什么是f(x)= 4x ^ 2-2x + x /(x-1/4)的局部极值?
Anonim

回答:

#f_(min)= f(1/4 + 2 ^( - 5/3))=(2 ^(2/3)+ 3 + 2 ^(5/3))/ 4。#

说明:

观察, #F(X)= 4×^ 2-2x + X /(X-1/4); RR- {1/4}中的x。#

#= 4倍^ 2-2x + 1 / 4-1 / 4 + {(X-1/4)+1/4} /(X-1/4); xne1 / 4#

#=(2X-1/2)^ 2-1 / 4 + {(X-1/4)/(X-1/4)+(1/4)/(X-1/4)}; xne1 / 4#

#= 4(X-1/4)^ 2-1 / 4 + {1+(1/4)/(X-1/4)}; xne1 / 4#

#:. F(X)= 4(X-1/4)^ 2 + 3/4 +(1/4)/(X-1/4); xne1 / 4#

现在,为 局部极值, #F'(X)= 0,# 和,

#f''(x)>或<0,“根据”f_(min)或f_(max),“resp。”#

#F'(X)= 0#

#rArr 4 {2(x-1/4)} + 0 + 1/4 {( - 1)/(x-1/4)^ 2} = 0 …(ast)#

#rArr 8(x-1/4)= 1 / {4(x-1/4)^ 2},或,(x-1/4)^ 3 = 1/32 = 2 ^ -5。

#rArr x = 1/4 + 2 ^( - 5/3)#

进一步, #(ast)rArr f''(x)= 8-1 / 4 {-2(x-1/4)^ - 3},“这样,”#

#F ''(1/4 + 2 ^( - 5/3))= 8 +(1/2)(2 ^( - 5/3))^ - 3> 0#

#“因此,”f_(min)= f(1/4 + 2 ^( - 5/3))#

#=4(2^(-5/3))^2+3/4+(1/4)/(2^(-5/3))=2^2*2^(-10/3)+3/4+2^(-2)*2^(5/3)#

#=1/2^(4/3)+3/2^2+1/2^(1/3)=(2^(2/3)+3+2^(5/3))/4.#

从而, #f_(分钟)= F(1/4 + 2 ^( - 5/3))=(2 ^(2/3)+ 3 + 2 ^(5/3))/ 4#

享受数学。!