1樓:匿名使用者
x(√x+√y)=3√y(√x+5√y)
=>x+√(xy)-3√(xy)-15y=0=>(√x-5√y)(√x+3√y)=0
x>0,y>0=>√x+3√y>0
=>√x-5√y=0 =>x=25y
=>(2x+(√xy)+3y)/(x+(√xy)-y)=(50y+5y+3y)/(25y+5y-y)=2(a^3n+a^-3n)/(a^n+a^-n)=a^(2n)-1+a^(-2n)=√2+1-1+1/(√2+1)=2√2-1
2樓:匿名使用者
√x(√x+√y)=3√y(√x+5√y)
√x*√x+√x*√y=3√y*√x+√y*15√y
x+√(xy)=3√(xy)+15y
x-2√(xy)=15y
x-2√(xy)+y=16y
(√x-√y)^2=16y
√x-√y=4√y
√x=5√y
x=25y
[2x+(√xy)+3y)]/[x+(√xy)-y]
=[2*25y+√(25y*y)+3y]/[25y+√(25y*y)-y]
=(50y+5y+3y)/(25y+5y-y)
=58y/29y
=2 (a^3n+a^-3n)/(a^n+a^-n)
=(a^n+a^-n)(a^2n+a^-2n-1)/(a^n+a^-n)
=a^2n+a^-2n-1
=√2+1-1+1/(√2+1)
=√2 +√2+1
=2√2-1
x^1/2+x^-1/2=3,求(x^3/2+x^-3/2-3)/(x^2-x^-2-2)
x^1/2+x^-1/2=3
(x^1/2+x^-1/2)^2=9
x^1+x^-1+2=9
x^1+x^-1=7
x^1+x^-1=7
x^1-2+x^-1=7-2
(x^1/2-x^-1/2)^2=5
(x^1/2-x^-1/2)^2=5
x^1/2-x^-1/2=±√5
當x^1/2-x^-1/2=√5,x^1+x^-1=7時
(x^3/2+x^-3/2-3)/(x^2-x^-2-2)
=[(x^1/2+x^-1/2)(x+x^-1-1)-3]/[(x^1+x^-1)(x^1-x^-1)-2]
=[3*(7-1)-3]/[7(x^1/2+x^-1/2)(x^1/2-x^-1/2)-2]
=15/[7*3*(x^1/2-x^-1/2)-2]
=5/[7*(x^1/2-x^-1/2)-2]
=5/[7*√5-2]
=5/(7√5-2)
=5(7√5+2)/(7√5-2)(7√5+2)
=(35√5+10)/241
當x^1/2-x^-1/2=-√5,x^1+x^-1=7時
(x^3/2+x^-3/2-3)/(x^2-x^-2-2)
=[(x^1/2+x^-1/2)(x+x^-1-1)-3]/[(x^1+x^-1)(x^1-x^-1)-2]
=[3*(7-1)-3]/[7(x^1/2+x^-1/2)(x^1/2-x^-1/2)-2]
=15/[7*3*(x^1/2-x^-1/2)-2]
=5/[7*(x^1/2-x^-1/2)-2]
=5/[7*(-√5)-2]
=-5/(7√5+2)
=-5(7√5-2)/(7√5-2)(7√5+2)
=(10-35√5)/241
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