Question 631470
Use the difference of two squares formula
{{{a^2-b^2=(a-b)(a+b)}}}
{{{16x^4-81y^4=4^2(x^2)^2-9^2(y^2)^2=(4x^2)^2-(9y^2)^2=(4x^2-9y^2)(4x^2+9y^2)=((2x)^2-(3y)^2)(4x^2+9y^2)=(2x-3y)(2x+3y)(4x^2+9y^2)}}}
Answer: a. {{{(2x+3y)(2x-3y)(4x^2+9y^2)}}}