For this case we must solve the following product:
![-7a ^ 2 (3a ^ 3-4a ^ 5)](https://tex.z-dn.net/?f=-7a%20%5E%202%20%283a%20%5E%203-4a%20%5E%205%29)
We know that, by definition, the distributive property states that:
![a (b + c) = ab + ac](https://tex.z-dn.net/?f=a%20%28b%20%2B%20c%29%20%3D%20ab%20%2B%20ac)
Also, by definition, we know that:
![x ^ n * x ^ m = x ^ {m + n}](https://tex.z-dn.net/?f=x%20%5E%20n%20%2A%20x%20%5E%20m%20%3D%20x%20%5E%20%7Bm%20%2B%20n%7D)
On the other hand, we have to:
![+ * - = -\\- * - = +](https://tex.z-dn.net/?f=%2B%20%2A%20-%20%3D%20-%5C%5C-%20%2A%20-%20%3D%20%2B)
So:
Resolving, multiplying term by term, taking into account the previous definitions, we have:
![-7a ^ 2 (3a ^ 3-4a ^ 5) = - 21a ^ 5 + 28a ^ 7](https://tex.z-dn.net/?f=-7a%20%5E%202%20%283a%20%5E%203-4a%20%5E%205%29%20%3D%20-%2021a%20%5E%205%20%2B%2028a%20%5E%207)
Answer:
option b