15x^4 - 150x^2 + 135 ? set to 0 and solve

I need to set this equation to 0 and solve for x but I dont know how to? please help!

15x^4 - 150x^2 + 135 = 0

Factor out a 15 and divide by 15.
15(x^4 - 10x^2 + 9) = 0
x^4 - 10x^2 + 9 = 0

Rewrite to make it simpler. x^4 = (x^2)^2 by the way.
(x^2)^2 - 10(x^2) + 9 = 0

Let X = x^2 Substitute that in.
X^2 - 10X + 9 = 0

Factor.
(X - 1) (X - 9) = 0

Put x^2 back in for X.
(x^2 - 1) (x^2 - 9) = 0

Factor the difference of squares.
(x - 1)(x + 1)(x + 3)(x - 3) = 0

The solutions are
x = -3, -1, 1, 3

I hope this helps.

15x^4 - 150x^2 + 135 = 0
15(x^4 - 10x^2 + 9) = 0
x^4 - 10x^2 + 9 = 0
(x² - 1)²(x² - 9)² = 0

If the product of two terms equals zero, then one or both terms equal zero.

If (x² - 1)² = 0,
x² - 1 = 0
x² = 1
x = √1
x = ± 1

If (x² - 9)² = 0,
x² - 9 = 0
x² = 9
x = √9
x = ± 3

x { ± 1, ± 3 }
¯¯¯¯¯¯¯¯¯¯¯

♥♦♣♠
►►►set to zero, so equate it to 0:
15x^4 - 150x^2 + 135 = 0
.....................let's then factorize the expression;
( 5x² - 5 ) • ( 3x² - 27 ) = 0
.................................but first, let's check if the factors are corect;
.................................= ( 5x² ) ( 3x² ) + ( 5x² ) ( -27 ) + ( -5 ) ( 3x² ) + ( -5 ) ( -27 )
.................................= 15x^4 - 135x² - 15x² + 135
.................................= 15x^4 - 150x² + 135................okay, we got it right !
.....................now, any of the expression should be equal to zero;
5x² - 5 = 0...............&..............3x² - 27 = 0
.....................add 5 to both sides of the left equation,
.....................add 27 to both sides of the right equation;
5x² - 5 + 5 = 0 + 5...............&..............3x² - 27 + 27 = 0 + 27
5x² = 5...............&..............3x² = 27
.....................divide both sides of the left equation by 5,
.....................divide both sides of the right equation by 3;
5x² / 5 = 5 / 5...............&..............3x² / 3 = 27 / 3
x² = 1...............&..............x² = 9
.....................get the squareroot of both sides of both equations;
√x² = √1...............&..............√x² = √9
x = 1...............&..............x = 3
░░░░░░░░░░░░░░░░░░░░

☼☼☼☺☺☺☼☼☼...let's check :

for x = 1;
15 ( 1 )^4 - 150 ( 1 )^2 + 135 = 0
15 ( 1 ) - 150 ( 1 ) + 135 = 0
15 - 150 + 135 = 0
150 - 150 = 0
0 = 0...................b i n g o ! ! !

for x = 3;
15 ( 3 )^4 - 150 ( 3 )^2 + 135 = 0
15 ( 81 ) - 150 ( 9 ) + 135 = 0
1,215 - 1,350 + 135 = 0
1,350 - 1,350 = 0
0 = 0...................b i n g o ! ! !

☼☼☼☺☺☺☼☼☼☺☺☺