first off, "10a รท 5b" is different from "10a รท (5b)"
Because we are writing divisions and fractions in a straight line like this, you need to be clear on which numbers are the denominators and which aren't. If there are more than 1 element, then group 'em together in a bracket. Else, they are considered to be separated and only the first one is the denominator.
ex:
"10a รท 5b" legit means "10 ร a รท 5 ร b" so only 5 is dividing 10a and b is later multiplied.
"10a รท (5b)" means 5 and b are together and both are the denominator in the fraction with numerator 10a.
if 2 is a coefficient of (1+2), then (1+2) has to go together with 2 under the line, like this
"6 รท (2(1+2))"
no parenthesis means only 2 is dividing 6 which is then multiplied with (1+2) after.
If we're to translate "6 รท 2(1+2)" into the bigger format it would look like this:
And then "6 รท (2(1+2))" (which is what you mean), would look like this:
โ โ โ โ โ 6
โโโโ = 1
2 (1+2)