若m,n是方程x²-3x-5=0的两个实数根,求m²+2n²-3n的值
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若m,n是方程x²-3x-5=0的两个实数根,求m²+2n²-3n的值
若m,n是方程x²-3x-5=0的两个实数根,求m²+2n²-3n的值
若m,n是方程x²-3x-5=0的两个实数根,求m²+2n²-3n的值
m,n是方程x²-3x-5=0的两个实数根,
所以m²-3m-5=0
n²-3n-5=0
m+n= -5
m²+2n²-3n
=m²-3m-5+n²-3n-5+n²-3n-5+15+3m+3n
=15+3×(-5)
=0
mn=-5
m+n = 3
(105±3√29)/4