Chapter 12 - Sequences; Induction; the Binomial Theorem - 12.2 Arithmetic Sequences - 12.2 Assess Your Understanding - Page 814: 24

$a_n=(n-1)\cdot\pi.$ $a_{51}=50\cdot\pi.$

We know that $a_n=a_1+(n-1)d.$ where $d$=common difference and $a_1$= the first term Hence, here we have $a_n=0+(n-1)\cdot\pi\\=(n-1)\cdot\pi.$ Therefore $a_{51}=(51-1)\cdot\pi\\=50\cdot\pi.$