✔ 最佳答案
1. 令 x^2 + px + q = 0 兩根是 m . n =>
求做 以 m^2 . n^2 當作根的方程式
=> m^2 + n^2 = ( m + n )^2 - 2mn = - p^2 - 2q
=> m^2 * n^2 = ( mn )^2 = q^2
=> x^2 + ( p^2 + 2q ) x + q^2 = 0
2. ( x^2 - 5x + 2 ) = ( x - α) ( x - β)
= x^2 - ( α+ β) x + αβ
=> α+β = 5 . αβ = 2
1 / (2α - 1 ) + 1 / ( 2β - 1 )
= ( 2β - 1 + 2α - 1 ) / ( 2α - 1 )( 2β - 1 )
= 2 ( α+β - 1 ) / [ 4αβ - 2 ( α+β ) + 1 ]
= 8 / [ 8 - 10 + 1 ] = - 8
[ 1 / (2α - 1 )] *[ 1 / ( 2β - 1 )] = 1 / [ 4αβ - 2 ( α+β ) + 1 ]
= 1 / - 1 = - 1
=> x^2 + 8x - 1 = 0