\frac{3x}{3y}=\frac{\not{3}x}{\not{3}y}

\(\displaystyle \frac{3x}{3y}=\frac{\not{3}x}{\not{3}y}=\frac{x}{y}\)

But if I try with a binomial it only crosses out the parenthesis.

\(\displaystyle \frac{3\not{(a+b)}}{\not{(a+b)}}=3\)

Any ideas would be awesome.

TES