View Full Version : Sequence euation
arbee
Feb 8, 2011, 06:24 PM
the givn is 3 -6 12 -24 find the sequence equation
arbee
Feb 8, 2011, 06:26 PM
jcaron2
Feb 8, 2011, 07:39 PM
Each number is -2 times the previous. So you know it'll be something like
A_n=c \cdot (-2)^n,
where A_n is the nth term and c is some constant that you have to figure out. It's simple enough to figure out what c is: just plug in the values for the first number.
3=c \cdot (-2)^1
\frac{3}{-2^1}=c
c=-\frac{3}{2}
So
A_n=-\frac{3}{2} \cdot (-2)^n
or to simplify a little more
A_n=3 \cdot \frac{(-2)^n}{-2}
A_n=3 \cdot (-2)^{n-1}
galactus
Feb 9, 2011, 06:46 AM
It is rather obvious that the numbers are multiples of 3.
Try 3\cdot (-2)^{n}, \;\ n=0,1,2......
What's the next number?