Question

What is the greatest common factor of 42 and 63

Answer 1

$42|2\\21|3\\.\ 7|7\\.\ 1|\\42=2\times\fbox3\times\fbox7\\\\63|3\\21|3\\.\ 7|7\\.\ 1|\\63=\fbox3\times3\times\fbox7\\\\GCF(42;\ 63)=\fbox3\times\fbox7=\boxed{\boxed{21}}$