已知：㎡-5m-1=0,求：2㎡-5m+1⼀㎡

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2024-12-21 03:27:37

推荐回答（1个）

回答1：

㎡-5m-1=0,
㎡=5m+1
㎡-5m-1=0
用公式法解得
m=5+√5^2-4*1*(-1)/2=5+√29/2
或m=5-√5^2-4*1*(-1)/2=5-√29/2
2㎡-5m+1/㎡
=㎡+㎡-5m+1/㎡
=5m+1+㎡-5m+1/㎡
=㎡+2/㎡
=1+2/㎡
=1+2/(5m+1)
（1）当m=5+√29/2
原式=1+2/(5m+1)
=1+2/(5（5+√29/2）+1)
=1+4/(25+5√29+2)
=1+4/(27+5√29)
=1+4(27-5√29)/(27^2-(5√29)^2)
=1+4(27-5√29)/(27^2-25*29)
=1+4(27-5√29)/(27^2-(27-2)(27+2))
=1+4(27-5√29)/(27^2-27^2+2^2)
=1+4(27-5√29)/4
=1+27-5√29
=28-5√29
（2）当m=5-√29/2
原式=1+2/(5m+1)
=1+2/(5（5-√29/2）+1)
=1+4/(25-5√29+2)
=1+4/(27-5√29)
=28+5√29