simplify (x+3/√2-3x)

recall that (a-b)(a+b) = a^2-b^2

(x+3)/(√2-3x) * (√2+3x)/(√2+3x)
= (x+3)(√2+3x)/(2-9x^2)

or something, depending on whether you were sloppy with your parentheses.