用公式法解下列方程. (要用公式法)①x²+√6 x=-2√3-√2 x ②mnx²-(m²+n²)x+mn=0
用公式法解下列方程. (要用公式法)
①x²+√6 x=-2√3-√2 x
②mnx²-(m²+n²)x+mn=0
x²+√6 x=-2√3-√2 x
x²+(√6+√2) x+2√3=0
x1={-(√6+√2)+√[(√6+√2)^2-4*2√3]}/2
=-√6
x2={-(√6+√2)-√[(√6+√2)^2-4*2√3]}/2
=-√2
mnx²-(m²+n²)x+mn=0
判别式=(m²+n²)^2-4*mn*mn
=(m²-n²)^2
x1=[(m²+n²)+|(m²-n²)|]/2mn
x2=[(m²+n²)-|(m²-n²)|]/2mn
此时有两种情况,当|m|>|n|时,|(m²-n²)|=m²-n²
x1=[m²+n²+m²-n²]/2mn=m/n
x2=[m²+n²+n²-m²)]/2mn=n/m
当|m|x1=[m²+n²-m²+n²]/2mn=n/m
x2=[m²+n²-n²+m²)]/2mn=m/n
综上得出,n,m无论何值,x总有固定解x1=n/m,x2=n/m
公式法带入公式就可以计算了
x=(-b±√b^2-4ac)/2a
剩下的就自己计算了吧..
1、
x²+(√6+√2)x+2√3=0
a=1,b=√6+√2,c=2√3
所以△=b²-4ac=6+2√12+2-8√3
=6-2√12+2
=(√6-√2)²
所以x=[-(√6+√2)±(√6-√2)]/2
-(√6+√2)-(√6-√2)=-2√6
-(√6+√2)+(√6-√2)=-2√2
所以x1=-√6,x2=-√2
2、
a=mn,b=-(m²+n²),c=mn
所以△=m^4+2m²n²+n^4-4m²n²
=m^4-2m²n²+n^4
=(m²-n²)²
所以=[(m²+n²)±(m²-n²)]/2mn
[(m²+n²)-(m²-n²)]/2mn=2n²/2mn=n/m
[(m²+n²)+(m²-n²)]/2mn=2m²/2mn=m/n
所以x1=n/m,x2=m/n