Answer:
C-D is:
![\mathbf{4b^4 -2a^b^2 -6b^4}](https://img.qammunity.org/2022/formulas/mathematics/college/3831adetq5kwo0vlsiuybttzccsyz0oqmx.png)
Explanation:
We are given:
![C = 7a^4+ + 5a^2b2 - 3b^4\\D=5a^4 + 7a^2b^2 + 3b^4](https://img.qammunity.org/2022/formulas/mathematics/college/tt3nk71e7jnck59v8gc4fpuycbzohe1x4m.png)
We need to find C-D.
Finding C-D we actually have to subtract D from C
So, finding C-D
![C-D\\= 7a^4+ + 5a^2b2 - 3b^4-(5a^4 + 7a^2b^2 + 3b^4)\\=7a^4+ + 5a^2b2 - 3b^4-5a^4-7a^2b^2-3b^4](https://img.qammunity.org/2022/formulas/mathematics/college/33v2tgiu0a7wjztv5n7ukgldgo9kdvzdpj.png)
Now, combining the like terms.
Like terms are those that have same variables and exponents.
In our case,
![7a^4\: and\: 3b^4, 5a^2b^2\: and\: -7a^b^2, -3b^4\:and\:-3b^4](https://img.qammunity.org/2022/formulas/mathematics/college/kt15hru4dtrorzcflm6l7lt3olb026hk3w.png)
![=7a^4 - 3b^4+5a^2b^2 -7a^b^2 -3b^4-3b^4\\=4b^4 -2a^b^2 -6b^4](https://img.qammunity.org/2022/formulas/mathematics/college/lkyxhul8molt41g7eimaercb2kaef0zqmd.png)
So, we get C-D is:
![\mathbf{4b^4 -2a^b^2 -6b^4}](https://img.qammunity.org/2022/formulas/mathematics/college/3831adetq5kwo0vlsiuybttzccsyz0oqmx.png)