## Algebra 1: Common Core (15th Edition)

The explicit formula is $a_{n}$=3 $\times$ (-4$)^{n-1}$
You have to use the explicit formula. The explicit formula is $a_{n}$=$a_{1}$ $\times$ (r$)^{n-1}$. The starting value is 3 so it is $a_{1}$. You have the sequence 3,-12,48 so use the common ratio formula(r=$\frac{{a_{2}}}{{a_{1}}}$) r=$\frac{-12}{3}$=-4 and r=$\frac{48}{-12}$=-4.So the common ratio is -4.Substitute the value of a1 and R into the explicit formula: The explicit formula is $a_{n}$=3 $\times$ (-4$)^{n-1}$