Answer :

Hippalectryon
36=6^2,64=8^2 and 96=6*8*2
hence we see using the formula (a+b)^2=a^2+2ab+b^2 that -36a^2-96ab-64b^2=-(6a+8b)^2

Edit : oops I didn't see the last part was 64ab^2 and not 64b^2, disregard the answer
Panoyin
-36a² - 96ab - 64ab²
-36a² - 48ab - 48ab - 64ab
(-6a - 8b)(6a + 8b)