a . \(\left(x+y+4\right)\left(x+y-4\right)=\left(x+y\right)^2-4^2\)
b . \(\left(x-y+6\right)\left(x+y-6\right)=x^2-\left(y-6\right)^2\)
c . \(\left(y+2z-3\right)\left(y-2z-3\right)=\left(y-3\right)^2-\left(2z\right)^2\)
d . \(\left(x+2y+3z\right)\left(2y+3z-x\right)=\left(2y+3z\right)^2-x^2\)