Question 1085363
The first needs an exponent of n-1 to make the 3^(n-1)=3^0 or 1 and the product 2*1=2.  Even numbered terms will have odd-numbered exponents which will make even numbered terms negative.  Of the possibilities a and b, b would make the first term negative, so it has to be (a)
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16 to 1/9 in two terms suggests 4^2 to 1/3^2
The intermediate term might be 4/3
16*(1/12)=4/3
4/3*(1/12)=1/9
+/-4/3 is the answer, since the second term could be positive or negative and this series be what it is.
(a)
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a4=a1+3d
a10=a1+9d
The difference between the two is -84, which is 6d, so d=-84/6=-14
a22=a10+12d or a10-168 or -11-168=-179
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a1+(n-1)d, and d is -7
an=-26-7n from n=0 to 5,  NOTE:  I will assume the fifth term is -54, not 54