X marks the spot

Algebra Level pending

4 , 9 , x , 37 4, 9, x, 37 is a quadratic sequence.

Solve for x x .


The answer is 20.

Meet Trivedi by Meet Trivedi , 23, South Africa

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2 solutions

Vince Policarpio
Apr 12, 2014
  1. First difference: 9 - 4 = 5, (x-9), (37-x)
  2. Second difference: (x-9) - 5, (37-x) - (x-9). This is the quadratic sequence.
  3. Then (x-9) - 5 = (37-x) - (x-9) or x = 20. (Q.E.D.)
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Venture Hi
Apr 8, 2014

The quad sequence is4,9,x,37 Next, find the sequence after taking the difference between each number. 9-4, x-9,37-x Again, take the difference among the items in the sequence and set them equal to one another. (x-9)-5= (37-x)-(x-9) Solve for x. 3x=60 and x=20

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