SOLUTION: The first term of sequnce is x. To get the next term multiply the previous term by 2 and add 1.the third term of the sequence is 21.find the value of x. Plzz help me find the answe

Question 830793: The first term of sequnce is x. To get the next term multiply the previous term by 2 and add 1.the third term of the sequence is 21.find the value of x. Plzz help me find the answer...its 4.5 in the book gcse
Answer by JulietG(1812) (Show Source): You can put this solution on YOUR website!
Your sequence is:
(x, 2x + 1, 21)
You can work this backward.
Find the middle number first.
21 - 1 = 2x
20 = 2x
10 = x
.
Now take the 10 and work backward with the same formula.
10 - 1 = 2x
9 = 2x
4.5 = x
.
Let's plug it in to make certain.
4.5 * 2 = 9, plus 1 = 10
10 * 2 = 20, plus 1 = 21
Success!
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