factorisation (1 Viewer)

[stressedadfff]

hey guys, how would i factorise the following to show 4 + 3x^2-x^4= (4-x^2)(1+x^2)

 

[B1andB2]

let u=x^2 to reduce the equation
LHS= (-u+4)(u+1) by cross method
sub u back in