Reflection of P(a, b) in x-axis followed by reflection in origin is :

1. (a, b)

2. (-a, -b)

3. (-a, b)

4. (-a, -b)

We know that,

On reflecting in x-axis the sign of y co-ordinate changes.

Let on reflection in x-axis point P(a, b) becomes P'.

P(a, b) ⇒ P'(a, -b).

We know that,

On reflecting in origin the sign of both x and y co-ordinate changes.

Let on reflection in origin point P'(a, -b) becomes P".

P'(a, -b) ⇒ P"(-a, b).

Hence, Option 3 is the correct option.