Question

a) 16x^4-81 б)x^2-x-y^2-y

Answer 1

$16x^4-81=(4x^2)^2-9^2=(4x^2-9)(4x^2+9)=(2x-3)(2x+3)(4x^2+9)\\x^2-x-y^2-y=(x^2-y^2)-(x+y)= (x+y)(x-y)-(x+y)=(x+y)(x-y-1)$