If you typed the equation correctly, this is the way I interpret it.
1/x + 12 = 3x/3x^2 + 36
On the right side, the 3x terms cancel each other out.
1/x + 12 = 1/x + 36
To get x out of denominator, multiply both sides by x.
1 + 12x = 1 + 36x
Get like terms on the same side of the equation by subtracting 1 and 12x from both sides.
0 = 24x
x = 0
However, this does not check out when you substitute that value into the equation. I see no solution to this equation as you have typed it.
I hope this helps. Thanks for asking.
1/x+12=3x/3x^2+36
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