中4附數...急

Method 1
9x(4次)-40x(2次)+16=0
9 x^4 - 40 x^2 + 16 = 0
( 9 x^2 - 4 ) ( x^2 - 4 ) = 0
( 9 x^2 - 4 ) = 0 or ( x^2 - 4 ) = 0
( 3x + 2 ) ( 3x - 2 ) = 0 or ( x + 2 ) ( x - 2 ) = 0
x = - 2 / 3 or 2 / 3 or - 2 or 2

Method 2
9 x^4 - 40 x^2 + 16 = 0
Let y = x^2
9 y^2 - 40 y + 16 = 0
( 9y - 4 ) ( y - 4 ) = 0
9y - 4 = 0 or y - 4 = 0
y = 4 / 9 or y = 4
and y = x^2, therefore,
x^2 = 4 / 9 or x^2 = 4
so that, x = - 2 / 3 or 2 / 3 or - 2 or 2

LET Y=x^2
9y^2-40y+16=0
(y-4)(9y-4)=0
y=4OR4/9
x^2=4OR4/9
X=-2,2,-2/3,2/3