## Precalculus (6th Edition) Blitzer

a. $-6n+8$ b. $-172$ c. $-2550$
a. Based on the given sequence, we have $a_1=2, d=-4-2=-6$ Thus $a_n=a_1+(n-1)d=2-6(n-1)=-6n+8$ b. For $n=30$, we have $a_{30}=-6(30)+8=-172$ c. For the sum, we have $S_n=\frac{n(a_1+a_n)}{2}$ and $a_{30}=\frac{30(2-172)}{2}=-2550$