Factorise: 

$x^4-5x^2+4$

Factorise: 

$x^4-10x^2+9$

Factorise: 

$a^4-7a^2{b}^2+b^4$

Factorise: 

$a^4+2a^2{b}^2+9b^4$

Factorise: 

$a^4+a^2{b}^2+25b^4$

Factorise: 

$8x^3+343y^3$

Factorise: 

$216a^3+\frac{b^3}{343}$

Factorise: 

$a^3+\frac{1}{27a^3}$