Question

Solve for x : 1 + 4 + 7 + 10 + ... + x = 590 .
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Answer 1

I hope your doubt is clear buddy

Answer 2

Answer:

$1 + 4 + 7 + 10 + x + x = 590 \\ 22 + 2x = 590 \\ 2x = 590 - 22 \\ 2x = 568 \\ x = \frac{568}{2} = 284$

so, the numbers are

1+4+7+10+284+284

hope you understand