Question 852439
x^4 - 10x^2 + 9 = 0
To factor, we know that the first factor will be x^2
(x^2     )(x^2   )
The second number factors to 9 -- so it's either 9,1 or 3,3.  3 +/- 3 is 6 or 0, so that's not it.  Therefore, it's 9 and 1.
(x^2   9)(x^2   1)
To find the correct sign, look at the middle number.  What combination of +9, -9 and +1, -1 will equal -10 when added?
(x^2-9)(x^2-1)
Put them to zero to find the possible X solutions.
x^2-9=0
Add 9 to each side
x^2=9
x=3 or -3 (when you square it, either works)
The second solution
x^2-1=0
Add 1 to each side
x^2=1
x= 1 or -1