Maths一問...*= ] 快~

x^4 - 24x^2 - 25=0

(x^2)^2 - 24(x^2) - 25=0

(cross method)

(x^2 - 25) (x^2+1)=0

x^2 - 25=0 or x^2+1=0

x^2=25 or x^2= -1(rejected) (because 開方 -1 cannot be calculated)

x=+5 or x= -5

The solutions are x=5 or x= -5

x^4 - 24x^2 -25= 0

x^4 - 24x^2 = 25

x^2(x^2 - 24) = 25

x^2= 25 or x^2 - 24=25

x=+5, -5 or x^2= 49
x = +7(rejected) , -7(rejected)

So, x= +5 or -5

y = x ^ 2
y^2 - 24y - 25 = 0
y = (24 +/- (24^2 + 4*25)^0.5 ) / 2
y = 12 +/- 119^0.5
x = +/-(12+119^0.5) or x = +/-(12-119^0.5)

y = 1.09 or y = 22.91
x = 1.04 or x = -1.04 or x = 4.79 or x = -4.79

2006-11-01 22:22:55 補充：
sorry should be y = 12 /- 13 in line 4y = 25 or y = -1real roots:x = 5 or x = -5

for y = x^2
y^2-24y-25 = 0
y = -1 or 25

x^2 = -1 (impossible)

x^2 = 25
x = 5

2006-11-01 22:15:09 補充：
x = 5 or -5

x^4 - 24x^2 -25= 0

(x-25) (x+1)=0

x=25
or
x=-1
Must correct~

x^4 - 24x^2 -25= 0
(x-25)(x+1)=0
x=25 or -1

2006-11-01 22:13:07 補充：
SOR, 看錯題目, 做錯了

x^4 - 24x^2 -25= 0
(x^2 + 1)(x^2 - 25) = 0

x^2 + 1 = 0
x^2 = -1
no real root

or

x^2 - 25 = 0
x^2 = 25
x = -5 or +5