F.4 Quadratic Function [復制鏈接]

If x and y are the roots of the equation5x^2+7x+2=0,find, without solving the equation, the values of

1)     x^4-y^4
2)     x^6-y^6

if x and y 係o個條equ o既root...
即係 x + y = -7/5
    xy = 2/5

x^4 - y^4
= ( x^2 + y^2 ) ( x ^2 - y^2)
= [ (x+y)^2 -2xy] (x+y)(x-y)
consider (x-y),

x-y = 開方 ( x-y)^2
    = 開方 [x^2+y^2 - 2xy]
    = 開方 [ (x+y)^2 -4xy]

呢個得o既話.....
第二part 唔會難....

引用第1樓someone於2007-09-11 20:36發表的“”:
if x and y 係o個條equ o既root...
即係 x + y = -7/5
    xy = 2/5
x^4 - y^4
.......

其實x同y係2個maths 既symble

引用第2樓dinlo於2007-09-11 20:55發表的“”:
其實x同y係2個maths 既symble

唔明你想講咩

引用第3樓someone於2007-09-11 20:57發表的“”:
唔明你想講咩

用sum of roots去計

引用第4樓dinlo於2007-09-11 21:00發表的“”:
用sum of roots去計

我唔係咩?

someone咪係lor

係!我睇錯