Factorization by the Difference of squares Questions with Solutions

Algebraic expressions

$(1).\,\,$ Factorize $x^4+64$

$(2).\,\,$ Factorize $x^4+x^2+1$

$(3).\,\,$ Factorize $x^2-16$

$(4).\,\,$ Factorize $64x^2-121y^2$

$(5).\,\,$ Factorize $16a^4-81b^4$