Answer:
[tex]a _{n} = a _{1} + (n - 1)d \\ a _{41} = - 534 \\ a _{54} = - 708 \\ a _{41} = a _{1} + (41 - 1)d = - 534 \\ a _{1} + 40d = - 534 \: \: ...(1)\\ a _{54} = a _{1} + (54 - 1)d =- 708 \\ a _{1} + 53d = - 708 \: \: ...(2)[/tex]
Try to solve the similtanious equation to find the first term and the common difference, then use that information to figure out the 80th term... Update me if you need further help ...
