Ok umm I think
x^4 - 11x^2 + 28
Write - 11x^2 as a difference
x^4 - 4x^2 - 7x^2 + 28
Factor out x^2 from the expression
x^2 x (x^2 - 4) - 7x^2 + 28
Factor out - 7 from the expression
x^2 x (x^2 - 4) - 7 (x^2 - 4)
Factor out x^2 - 4 from the expression
(x^2 - 4) x (x^2 - 7)
Use a^2 - b^2= (a-b)(a+b) to factor the expression
(x-2) x (x + 2) x (x^2 - 7)
And that’s how it’s (x-2) x (x + 2) x (x^2 - 7) ..... yea and .-.