Question

1)(а-5)^2-16b^2
2)x^2-y^2-5x-5y
3) 27-x^9

Answer 1

$(a-5)^2-16b^2=(a-5)^2-(4b)^2=((a-5)-4b)((a-5)+4b) \\ x^2-y^2-5x-5y=(x-y)(x+y)-5(x-y)=(x-y)((x+y)-5) \\ 27-x^9=3^3-(x^3)^3=(3-x^3)(9+3x^3+x^6)$