Tính nhanh: 5) 58 – 58 x (6 + 54 – 60) 6) 32 + 63 x a x ( a x 1 – a : 1) + 32 x 8 + 32 7) (1 + 2 + 3 + 4 + .... + 9) x (21 x 5 – 21 – 4 x 21) 8) (9 x 7 + 8 x 9 – 15 x 9) : (1 + 3 + 5 + 7 + ........+ 17 + 19) 9) (2 + 4 + 6 + 8 + ... + 20) x (56 x 3 – 72 : 9 x 21)

Đáp án:

 

Giải thích các bước giải:

`5) 58 - 58 xx ( 6 + 54 - 60 )`

= `58 - 58 xx ( 60 - 60 )`

= `58 - 58 xx 0`

= `58 - 0`

= `58`

____________

`6) 32 + 63 xx a xx ( a xx 1 - a : 1 ) + 32 xx 8 + 32`

= `32 + 63 xx a xx 0 + 32 xx 8 + 32`

= `32 xx ( 1 + 8 + 1 )`

= `32 xx 10`

= `320` 

___________

`7) ( 1 + 2 + 3 + 4 +.........+ 9 ) xx ( 21 xx 5 - 21 - 4 xx 21 )`

= `( 1 + 2 + 3 + 4 +......+ 9 ) xx [ 21 xx ( 5 - 1 - 4 )]`

= `( 1 + 2 + 3 + 4 +.......+ 9 ) xx [ 21 xx 0 ]`

= `( 1 + 2 + 3 + 4 +........+ 9 ) xx 0`

= `0`

___________

`8) ( 9 xx 7 + 8 xx 9 - 15 xx 9 ) : ( 1 + 3 + 5 + 7 +...........+ 17 + 19 )`

= `[ 9 xx ( 7 + 8 - 15 )] : ( 1 + 3 + 5 + 7 +...........+ 17 + 19 )`

= `[ 9 xx 0 ] : ( 1 + 3 + 5 + 7 +...........+ 17 + 19 )`

= `0 : ( 1 + 3 + 5 + 7 +...........+ 17 + 19 )`

= `0` 

__________

`9) ( 2 + 4 + 6 + 8 +.........+ 20 ) xx ( 56 xx 3 - 72 : 9 xx 21 )`

= `( 2 + 4 + 6 + 8 +.........+ 20 ) xx ( 56 xx 3 - 8 xx 21 )`

= `( 2 + 4 + 6 + 8 +.........+ 20 ) xx ( 168 - 168 )`

= `( 2 + 4 + 6 + 8 +.........+ 20 ) xx 0`

= `0`