(3x^2+5)(-3x^2+5)-x^2(7x+8)(7x-8)-(8x)^2其中x=-2先化简,在求值我想对一下答案,因为我这一块学的不是很好,拜托了!

(3x^2+5)(-3x^2+5)-x^2(7x+8)(7x-8)-(8x)^2
=[5^2-(3x^2)^2]-x^2[(7x)^2-8^2]-(8x)^2
=(25-9x^4)-x^2(49x^2-64)-(8x)^2
=25-9x^4-49x^4+64x^2-64x^2
=25-58x^4
x=-2
原式=-903