Expression: $\left( 1+\sqrt{ 3 }i \right) \times \left( 1-\sqrt{ 3 }i \right)$
Use $\left( a-b \right)\left( a+b \right)={a}^{2}-{b}^{2}$ to simplify the product $1-3{i}^{2}$
By definition ${i}^{2}=-1$ $1-3 \times \left( -1 \right)$
Any expression multiplied by $-1$ equals its opposite $1+3$
Add the numbers $4$