已知m^2-5m-1=0,求2m^2-5m+(1/m)这道题能做吗

来源:学生作业帮助网 编辑:作业帮 时间:2024/11/16 07:30:39
已知m^2-5m-1=0,求2m^2-5m+(1/m)这道题能做吗
xJ0_vYj2HpP7l.BfwW)M7i$iW5+r<ܼ]dU#[ݕl}y*ozElg?lT@p.Tp*Hu$U,)*TDYM *].kǃ hCj :iPfprV0^>->K=&'-O 1OxoƉ7%'f˫ۡ^ϕ1=a} B/C0d]c.C0de~z,J;

已知m^2-5m-1=0,求2m^2-5m+(1/m)这道题能做吗
已知m^2-5m-1=0,求2m^2-5m+(1/m)这道题能做吗

已知m^2-5m-1=0,求2m^2-5m+(1/m)这道题能做吗
已知m^2-5m-1=0,
m^2-2*2.5m+2.5^2-2.5^2-1=0,
(m-2.5)^2=7.25,
m-2.5=√7.25,或 m-2.5=-√7.25,
m1=2.5+√7.25,m2=2.5-√7.25,

2m^2-5m+1/m^2=2*(2.5+√7.25)^2-5*(2.5+√7.25)+1/(2.5+√7.25)^2=
=2*(6.25+5√7.25+7.25)-(12.5+5√7.25)+1/(6.25+5√7.25+7.25)=
=12.5+10√7.25+14.5-12.5-5√7.25+1/(13.5+5√7.25)=
=14.5+5√7.25+(13.5-5√7.25)/(182.25-181.25)=
=14.5+5√7.25+13.5-5√7.25=
=28;
或者,当m=m2=2.5-√7.25,
2m^2-5m+1/m^2=2*(2.5-√7.25)^2-5*(2.5-√7.25)+1/(2.5-√7.25)^2=
=2*(6.25-5√7.25+7.25)-(12.5-5√7.25)+1/(6.25-5√7.25+7.25)=
=12.5-10√7.25+14.5-12.5+5√7.25+1/(13.5-5√7.25)=
=14.5-5√7.25+(13.5+5√7.25)/(182.25-181.25)=
=14.5-5√7.25+13.5+5√7.25=
=28;