Question

The fourth term of a sequence is 18.The term-to-term rule is:Subtract 3 then multiply by 3.What is the first term of the sequence?​

Answer 1

let the 1st term be x

then the second term will be 3(x-3)

then the 3rd term will be 3(3(x-3)-3)

then the fourth term will be 3(3(3(x-3)-3)-3)

given that 4 th term= 18

then

$3(3(3(x - 3) - 3) - 3) = 18 \\ = > (3(3(x - 3) - 3) - 3) = 6 \\ = > 3(3(x - 3) - 3) = 9 \\ = > (3(x - 3) - 3) = 3 \\ = > 3(x - 3) = 6 \\ = > x - 3 = 2 \\ = > x = 5 \\ - - - - - - - - - - - - - - - - - -$

hence we got the first term which is 5

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