Chapter 12 - Sequences; Induction; the Binomial Theorem - 12.2 Arithmetic Sequences - 12.2 Assess Your Understanding - Page 814: 28

$-390.$

We know that $a_n=a_1+(n-1)d.$ where $d$=common difference and $a_1$= the first term Here $a_1=5$ and $d=a_2-a_1=0-5=-5$ Hence, here we have $a_n=5+(n-1)\cdot(-5).$ Therefore $a_{50}=5+(80-1)\cdot(-5)\\=-390.$