已知不存在r上的连续函数ff(x)满足f(x)-3f(1/x)=x(x≠0),求不存在r上的连续函数ff(x)的解析式?


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展开全部解:(法一)直接用公式f'(x)=f(x)+1即 f'(x)-f(x)=1故f(x)=e^∫dx [ ∫ e^∫-dx dx +c]=e^x[-e^(-x)+c]=ce^x-1又f(0)=0得c=1故f(x)=e^x-1(法二)dy/dx=y+1故dy/(y+1)=dx积分ln|y+1|=x+lncy+1=ce^x又f(0)=0得c=1故f(x)=e^x-1已赞过已踩过你对这个回答的评价是?评论
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0:-1;if(n!==r)for(var i=0;i0&&function(t,e,n,r){var i=document.getElementsByClassName(t);if(i.length>0)for(var o=0;o展开全部dy/dx=y+1dy/(y+1)=dx两边积分得通解为ln|y+1|=x+C
y+1|=e^(x+c)即f(x)=-1±e^(x+C)∵f(0)=0∴取+号,0=-1+e^C,c=0∴f(x)=-1+e^x
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(1)求证:f(x)是偶函数(2)求证:f(x)是周期函数(3)若f(x)在[0,1]内是单调函数,求f(1/3)与f(1/6)的值高中数学会的说下谢谢!...
(1)求证:f(x)是偶函数(2)求证:f(x)是周期函数(3)若f(x)在[0,1]内是单调函数,求f(1/3)与f(1/6)的值高中数学 会的说下 谢谢!
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(1)将x=y=0代入 f(x+y)+f(x-y)=2f(x)f(y)得,f(0)+f(0)=2f(0)f(0),即2f(0)=2f(0)f(0),由f(0)≠0得,f(0)=1, 再将x=0代入f(0+y)+f(0-y)=2f(0)f(y)得, f(y)+f(-y)=2f(y), f(-y)=f(y),故f(x)是偶函数。(2)将y=1/2代入f(x+y)+f(x-y)=2f(x)f(y)得f(x+1/2)+f(x-1/2)=2f(x)f(1/2)=0.由f(1/2)=0 得 f(x+1/2)+f(x-1/2) =0.f(x+1/2)=-f(x-1/2) , 同理f(x-1/2)= f(x-1+1/2)=- f(x-1-1/2)= - f(x-3/2),故f(x+1/2)= -f(x-1/2) =f(x-3/2), 设y= x-3/2,则x=y+3/2,x+1/2=y+2,代入上式得f(y+2)=f(y),故f(x)是周期为2的周期函数。(3)设x=y代入f(x+y)+f(x-y)=2f(x)f(y)得f(2x)+f(0)=2f(x)f(x),f(2x) =2f(x)f(x)-1, 将x=1/2代入得f(1) =2f(1/2)f(1/2)-1=-1,即f(1) =-1,设y=2x代入f(x+y)+f(x-y)=2f(x)f(y)得,f(3x)+f(-x)=2f(x)f(2x),故f(3x)=2f(x)f(2x)-f(x)=f(x)( 2f(2x)-1)=f(x)( 4f(x)f(x)-3)=4f(x)f(x)f(x)-3f(x)将x=1/3代入上式得f(1)=4 f(1/3) f(1/3) f(1/3)-3 f(1/3),设a=f(1/3)得4a^3-3a+1=0,解得a=1/2,即f(1/3)=1/2,再x=1/6代入f(2x) =2f(x)f(x)-1得f(1/3) =2f(1/6)f(1/6)-1,设b=f(1/3)得2bb-1= f(1/3)=1/2, 4bb-3=0,b=√3/2. f(x)在[0,1]内单调t得f(1/6)=√3/2。
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收起(1)令y=0,等式变为:f(x)+f(x)=2f(x)f(0),所以f(0)=1;再x=0,等式化为:f(y)+f(-y)=2f(0)f(y),所以f(y)=f(-y),偶函数得证;(2)令y=1/2,等式化为:f(x+1/2)+f(x-1/2)=0;再x-1/2=z,则f(z)=-f(z+1)=f(z+2),周期函数,最小正周期T=2;(3)令x=1/3;y=1/6,等式为:f(1/3+1/6)+f(1/3-1/6)=2f(1/3)f(1/6),即f(1/6)[2f(1/3)-1]=0.因为单调,且f(0)=1>f(1/2)=0,即单调减函数,所以f(1/6)>f(1/3)>f(1/2)=0;f(1/3)=1/2;令x=y=1/3,等式为:f(1/6+1/6)+f(1/6-1/6)=2f(1/6)f(1/6),f(1/6)=√3/2.(1)将x=y=0代入 f(x+y)+f(x-y)=2f(x)f(y)得,f(0)+f(0)=2f(0)f(0),即2f(0)=2f(0)f(0),由f(0)≠0得,f(0)=1, 再将x=0代入f(0+y)+f(0-y)=2f(0)f(y)得, f(y)+f(-y)=2f(y), f(-y)=f(y),故f(x)是偶函数。(2)将y=1/2代入f(x+y)+f(x-y)=2f(x)f(y)得f(x+1/2)+f(x-1/2)=2f(x)f(1/2)=0.由f(1/2)=0 得 f(x+1/2)+f(x-1/2) =0.f(x+1/2)=-f(x-1/2) , 同理f(x-1/2)= f(x-1+1/2)=- f(x-1-1/2)= - f(x-3/2),故f(x+1/2)= -f(x-1/2) =f(x-3/2), 设y= x-3/2,则x=y+3/2,x+1/2=y+2,代入上式得f(y+2)=f(y),故f(x)是周期为2的周期函数。(3)设x=y代入f(x+y)+f(x-y)=2f(x)f(y)得f(2x)+f(0)=2f(x)f(x),f(2x) =2f(x)f(x)-1, 将x=1/2代入得f(1) =2f(1/2)f(1/2)-1=-1,即f(1) =-1,设y=2x代入f(x+y)+f(x-y)=2f(x)f(y)得,f(3x)+f(-x)=2f(x)f(2x),故f(3x)=2f(x)f(2x)-f(x)=f(x)( 2f(2x)-1)=f(x)( 4f(x)f(x)-3)=4f(x)f(x)f(x)-3f(x)将x=1/3代入上式得f(1)=4 f(1/3) f(1/3) f(1/3)-3 f(1/3),设a=f(1/3)得4a^3-3a+1=0,解得a=1/2,即f(1/3)=1/2,再x=1/6代入f(2x) =2f(x)f(x)-1得f(1/3) =2f(1/6)f(1/6)-1,设b=f(1/3)得2bb-1= f(1/3)=1/2, 4bb-3=0,b=√3/2. f(x)在[0,1]内单调t得f(1/6)=√3/2。 所以f(1/3)=1/2
f(1/6)=3/2这个我还真的忘了,都大学毕业工作几年了}

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