a) \(x^4-47x^2y^2+y^4=x^4+2x^2y^2+y^4-49x^2y^2\)
\(=\left(x^2+y^2\right)^2-\left(7xy\right)^2\)
\(=\left(x^2+y^2+7xy\right)\left(x^2+y^2-7xy\right)\)
b, \(x^4-98x^2y^2+y^4=x^4+2x^2y^2+y^4-100x^2y^2\)
\(=\left(x^2+y^2\right)^2-\left(10xy\right)^2\)
\(=\left(x^2+y^2+10xy\right)\left(x^2+y^2-10xy\right)\)
c, \(x^3-x=x\left(x^2-1\right)=x\left(x+1\right)\left(x-1\right)\)