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Bài 1:

`1.` Thay `x = 7, y = 9` vào biểu thức `(15 - x + 39x) : (5x + 5y)`: ta có

`(15 - 7 + 39 xx 7) : (5 xx 7 + 5xx9)`

`= (15 - 7 + 273) : (35 + 45)`

`= 281 : 80`

`=` `281/80`

`2.` Thay `x = 3` vào biểu thức `7x (x + 3) + 2x ( 5x - 8)`: ta có

 `7xx3 (3 + 3) + 2xx3 ( 5xx3 - 8)`

`= 7xx3xx6+2xx3xx7`

`= 126 + 42`

`= 168`

Bài 2. Tính

`1) 2010 - 2 × [486 - 2 × (49 - 6)]`

`2010 - 2 × [486 - 2 × (49 - 6)]`

`= 2010 - 2 × [486 - 2 × 43]`

`= 2010 - 2 × (486 - 86)`

`= 2010 - 2 × 400`

`= 2010 - 800`

`= 1210`

`2)``{504 - (25 × 8 + 70) : 27 + 6} : 125`

`= {504 - (200 + 70) : 27 + 6} : 125`

`= {504 - 270 : 27 + 6} : 125`

`= {504 - 10 + 6} : 125`

`= 500 : 125`

`= 4`

`3) [156 : (81 - 216 : 72) - 2] × 2012`

`[156 : (81 - 216 : 72) - 2] × 2012`

`= [156 : (81 - 3) - 2] × 2012`

`= [156 : 78 - 2] × 2012`

`= (2 - 2) × 2012`

`= 0 × 2012`

`= 0`

`4) 45 - [(8 × 15 - 60) : 15 + 6] : 2`

`45 - [(8 × 15 - 60) : 15 + 6] : 2`

`= 45 - [(120 - 60) : 15 + 6] : 2`

`= 45 - [60 : 15 + 6] : 2`

`= 45 - (4 + 6) : 2`

`= 45 - 10 : 2`

`= 45 - 5`

`= 40`

`5) [58 + 72 × 5 - (600 + 45)] × 12`

`[58 + 72 × 5 - (600 + 45)] × 12`

`= [58 + 360 - 645] × 12`

`= [418 - 645] × 12`

`= -227 × 12`

`= -2724`

`6) [(15 × 9 - 144 : 12) : 25] : 148 - 1`

`[(15 × 9 - 144 : 12) : 25] : 148 - 1`

`= [(135 - 12) : 25] : 148 - 1`

`= (123 : 25) : 148 - 1`

`= 123 : (25 × 148) - 1`

`= 123 : 3700 - 1`

`= 123/3700 - 1`

`= (123 - 3700) / 3700`

`= -3577/3700`

`7) 745 × (120 - 75) - 70`

`745 × (120 - 75) - 70`

`= 745 × 45 - 70`

`= 33525 - 70`

`= 33455`