To multiply these expressions, we can use the formula for the product of the difference of squares: (a^2 - b^2) = (a + b)(a - b).

First, let's apply this formula to the first two terms, (x+4)(x-4):
(x+4)(x-4) = x^2 - 4^2 = x^2 - 16

Next, let's apply the formula to the last two terms, (8-a)(8+a):
(8-a)(8+a) = 8^2 - a^2 = 64 - a^2

Now we have:
(x^2 - 16)(64 - a^2)

To multiply these two binomials, we can use the distributive property:
x^2 64 = 64x^2
x^2 (-a^2) = -a^2x^2
(-16) 64 = -1024
(-16) (-a^2) = 16a^2

Putting it all together, we get:
64x^2 - a^2x^2 - 1024 + 16a^2

Therefore, the expanded expression is:
64x^2 - a^2x^2 - 1024 + 16a^2