A=21 + 22 + 23 + 24 + .......+22010
A = ( 2 + 22 + 23 ) + ( 24 + 25 + 26 ) + ... + ( 22008 + 22009 + 22010 )
A = 14 + 23 . ( 2 + 22 + 23 ) + ... + 22007 . ( 2 + 22 + 23 )
A = 14 + 23 . 14 + ... + 22007 . 14
A = 14 . ( 1 + 23 + ... + 22007 )
A = 7 . 2 . ( 1 + 23 + ... + 22007 ) chia hết cho 7 vì cho thừa số 7
A=2+22+23+...+22010
A=(2+22+23)+...+(22008+22009+22010)
A=2.(1+2+22)+...+22008.(1+2+22)
A=2.7+...+22008.7
A=7.(2+...+22008) chia hết cho 7
A = 21 + 22 + 23 + 24 + ... + 22010
A = ( 21 + 22 + 23 ) + ( 24 + 25 + 26 ) + ... + ( 22008 + 22009 + 22010 )
A = 21 ( 1 + 2 + 4 ) + 24 ( 1 + 2 + 4 ) + ... + 22008 ( 1 + 2 + 4 )
A = 21 . 7 + 24 . 7 + ... + 22008 . 7
A = 7 . ( 21 + 24 + ... + 22008 ) chia hết cho 7