The answers are correct.
To represent disjoint intervals in interval notation, we only need to join each interval using a "union sign", or ∪.
So the required answer would be:
(-∞, -3/4) ∪ (2, +∞)
Parentheses have been used in the above cases (instead of square brackets) because in each of the 4 cases, the values of the limits are to be excluded from the interval.