Answer:
![C(n)=30-20n](https://img.qammunity.org/2022/formulas/mathematics/high-school/qoqzboweeiz0qo71yba01qvail5i85stqo.png)
Explanation:
Arithmetic sequence given in the question is,
10, -10, -30, -50........
Explicit formula of an Arithmetic sequence is given by,
![C(n)=C(1)+(n-1)d](https://img.qammunity.org/2022/formulas/mathematics/high-school/p5gdkruzffs2xjwwslh85yp5gbm7s4jj1l.png)
Here,
First term
number of terms
common difference
From the given sequence,
![C(1)=10](https://img.qammunity.org/2022/formulas/mathematics/high-school/77halmvf09icvz26its8qp17s7byydfnyp.png)
![d=-10-10](https://img.qammunity.org/2022/formulas/mathematics/high-school/rrahu7dv7imokqz5nwozzkhxjct8x7vxw2.png)
![=-20](https://img.qammunity.org/2022/formulas/mathematics/high-school/f4tle1dz02l7qm1dgcc7fx1kkx1nt05j8w.png)
Substitute the values in the formula,
![C(n)=10+(n-1)(-20)](https://img.qammunity.org/2022/formulas/mathematics/high-school/n83gu7j9pwocossju470uf8uysbq8n0ii8.png)
![C(n)=10-20n+20](https://img.qammunity.org/2022/formulas/mathematics/high-school/8zhu76dfeqx8rll7gz88ozsfjtilpwwgze.png)
![C(n)=30-20n](https://img.qammunity.org/2022/formulas/mathematics/high-school/qoqzboweeiz0qo71yba01qvail5i85stqo.png)