Solve for x>0 in the following arithmetic sequence 1^2,x^2,3^2.....

Answer 1

1 , x^2 , 9

x^2 - 1 = d
-x^2 + 9 = d
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0 + 8 = 2 d
d = 4
so
1 , 5 , 9

x = sqrt(5)