已知非零向量\(\overrightarrow {AB} \)与\(\overrightarrow {AC} \)满足\((\overrightarrow {AB} + \overrightarrow {AC} ){\rm{ }}\bullet {\rm{ }}(\overrightarrow {AB} - \overrightarrow {AC} ) = 0\),且\(\frac{{\overrightarrow {AB} }}{{|\overrightarrow {AB} |}}{\rm{ }}\bullet {\rm{ }}\frac{{\overrightarrow {AC} }}{{|\overrightarrow {AC} |}} = \frac{1}{2}\),则\(\vartriangle ABC\)为( ).