Expand $\left(x^3-3\right)\left(x^3+3\right)$.

Expand $\left(a^4-\frac{1}{5y}\right)\left(a^4+\frac{1}{5y}\right)$

Find the value of $(x+y)(x-y)\left(x^2+y^2\right)$.

Find the value of $\left(a^2+b^2\right)\left(a^4+b^4\right)(a+b)(a-b)$.

State whether the expression $x^2+8x+16$  is a perfect square or not.

State whether the expression $y^2+3y+9$ is a perfect square.

State whether the expression $4m^2-4m+1$ is a perfect square or not.

State whether the expression $4x^2-2+\frac{1}{4x^2}$ is a perfect square or not.

State whether the expression $m^2+6m+4$ is a perfect square or not.