f.4 quad. equation15marks!!!!!

2009-12-14 6:00 am
If α and βare the roots of the quad. equation 2x^2 - 6x+3=0 and α>β,find the value of the expressions.
(a) α^2+β^2
(b) (α-β)^2
(c) α-β
(d) α^4 - β^4

請詳列計算過程

回答 (1)

2009-12-14 6:18 am
✔ 最佳答案
2x^2 - 6x + 3 = 0
Sum of roots α+β = 6/2 = 3
Product of roots αβ = 3/2
(a) α^2 + β^2
= α^2 + β^2 + 2αβ - 2αβ
= (α + β)^2 - 2αβ
= 3^2 - 2(3/2)
= 6
(b) (α - β)^2
= α^2 + β^2 - 2αβ
= 6 - 2(3/2)
= 3
(c) (α - β)^2 = 3
α - β = √3 since α > β
(d) α^4 - β^4
= (α^2 - β^2)(α^2 + β^2)
= (α - β)(α + β)(α^2 + β^2)
= √3(3)(6)
= 18√3


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