Question

$\frac{78^{3} - 18^{3} }{78^{2} + 18^{2} + 78 \times 18 }$

Answer 1

${a}^{3} - {b}^{3} = (a - b)( {a}^{2} + ab + {b}^{2}) \\ \frac{ {a}^{3} - {b}^{3} }{ \:( {a}^{2} + ab + {b}^{2})} = (a - b) \\ = 78 - 18 = 60$