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Whats the pattern for 1 -3 9 ? 81 ? -243. ? ?

Guest Jan 15, 2015

Best Answer 

 #3
avatar+20025 
+10

Whats the pattern for 1 -3 9 ? 81 ? -243. ? ?

$$\begin{array}{lrcl}
n& & & \\
1& 1 & = & 3^0 \\
2& -3 &=& (-3)^1 \\
3& 9 &=& 3^2\\
4& -27 &=& (-3)^3 \\
5& 81 &=& 3^4\\
6&-243 &=& (-3)^5\\
7&729 &=& 3^6\\
8&-2187 &=& (-3)^7\\
\dots
\end{array}
\\
\small{\text{
The formula is: $(-3)^{n-1}$
}}$$

heureka  Jan 15, 2015
 #1
avatar
+5

the first item is 1 and the second item is -3 , the difference  between these two numbers are -3/1 =-3

the second item is  3 and the third item is 9, the difference between these two numbers are 9/-3=-3

so the common difference is -3 , the fourth  item should be =3x9=27 and the fifth item 81=-3x-27

so you can find the others by yourself .......... 

Guest Jan 15, 2015
 #2
avatar+90001 
+5

(-1)n+1(3)n-1    ....where n is the nth term.....

 

CPhill  Jan 15, 2015
 #3
avatar+20025 
+10
Best Answer

Whats the pattern for 1 -3 9 ? 81 ? -243. ? ?

$$\begin{array}{lrcl}
n& & & \\
1& 1 & = & 3^0 \\
2& -3 &=& (-3)^1 \\
3& 9 &=& 3^2\\
4& -27 &=& (-3)^3 \\
5& 81 &=& 3^4\\
6&-243 &=& (-3)^5\\
7&729 &=& 3^6\\
8&-2187 &=& (-3)^7\\
\dots
\end{array}
\\
\small{\text{
The formula is: $(-3)^{n-1}$
}}$$

heureka  Jan 15, 2015

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