tiính giá trị biểu thức a) 4/9 x 8/15 + 4/9 x 7/15 - 4/9 b) 3/10 x ( -4/9 + 2/5) - 3/10 x (5/9 + -3/5) c) -2/7 x (5/13 - 9/15) - 2/7 x 8/13

`a) 4/9 × 8/15 + 4/9 × 7/15 - 4/9`

`= 4/9 × (8/15 + 7/15 - 1)`

`= 4/9 × (1 - 1)`

`= 4/9 × 0`

`= 0`

`b) 3/10 × (-4/9 + 2/5) - 3/10 × (5/9 - 3/5)`

`= 3/10 × [(-4/9 + 2/5) - (5/9 - 3/5)]`

`= 3/10 × (-4/9 + 2/5 - 5/9 + 3/5)`

`= 3/10 × (-4/9 - 5/9  + 2/5+ 3/5)`

`= 3/10 × (-1 + 1)`

`= 3/10 × 0`

`= 0`

`c) -2/7 × (5/13 - 9/15) - 2/7 × 8/13`

`= -2/7 × (5/13 - 9/15) + (-2/7 × 8/13)`

`= -2/7 × (5/13 - 9/15 + 8/13)`

`= -2/7 × (1 - 3/5)`

`= -2/7 × 2/5`

`= -4/35`

`a)`

`4/9 xx 8/15 + 4/9 xx 7/15 - 4/9`

`= 4/9 xx ( 8/15 + 7/15 - 1 )`

`= 4/9 xx 0`

`= 0`

`b)`

`3/10 xx ( -4/9 + 2/5 ) - 3/10 xx ( 5/9 + {-3}/5 )`

`= 3/10 xx ( -4/9 + 2/5 - 5/9 + 3/5 )`

`= 3/10 xx [ ( -4/9 - 5/9 ) + ( 2/5 + 3/5 ) ]`

`= 3/10 xx ( -1 + 1 )`

`= 3/10 xx 0`

`= 0`

`c)`

`-2/7 xx ( 5/13 - 9/15 ) - 2/7 xx 8/13`

`= 2/7 xx ( 9/15 - 5/13 ) - 2/7 xx 8/13`

`= 2/7 xx ( 9/15 - 5/13 - 8/13 )`

`= 2/7 xx ( 9/15 - 1 )`

`= 2/7 xx ( -2/5 )`

`= -4/35`