Solve: 1/3a^2 - 1/a = 1/6a^2

If you mean:

1 / (3a^2) - 1/a=1 / (6a^2) we need a common denominator of 6a^2

2 / (6a^2) - 6a / (6a^2) = 1 / (6a^2), multiplying all terms by 6a^2 then:

2-6a=1 subtract 2 from both sides

-6a=-1 divide both sides by - 6

a=1/6