Bài 1 : Thực hiện phép tính :
a ) 13 . 75 + 25 . 13 – 120 b ) ( – 156 ) + ( – 175 ) + ║ – 156 ║ + 125
c ) 8 mũ 7 : 8 ³ [ 39 – ( 2 ³ . 3 – 21 ) ² ] : 3
bài 2 : Tìm số nguyên x , biết :
a ) 10 + ( 31 – x ) = 40 b ) ( ║ x ║ + 3 ) . 15 – 5 = 70
c ) 3 mũ x + 1 . 15 + 3 mũ x + 1 . 12 = 3 mũ 21
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Bài 1:
a, 13 . 75 + 25 . 13 – 120
= 13 . ( 75 + 25 ) – 120
= 13 . 100 – 120
= 1300 – 120
= 1180
b, ( -156 ) + ( -175 ) + | -156 | + 125
= ( -156 ) – 175 + 156 + 125
= ( 156 – 156 ) + ( 125 – 175 )
= -50
c, `8^7` : `8^3` . [ 39 – ( `2^3` . 3 – 21 )² ] : 3
= `8^4` . [ 39 – ( 8 . 3 – 21 )² ] : 3
= `8^4` . ( 39 – 3² ) : 3
= `8^4` . ( 39 – 9 ) : 3
= `8^4` . 30 : 3
= 4096 . 30 : 3
= 4096 . 10
= 40960
Bài 2:
a, 10 + ( 31 – x ) = 40
31 – x = 40 – 10
31 – x = 30
x = 31 – 30
x = 1
Vậy x = 1
b, ( | x | + 3 ) . 15 – 5 = 70
( | x | + 3 ) . 15 = 70 + 5
( | x | + 3 ) . 15 = 75
| x | + 3 = 75 : 15
| x | + 3 = 5
| x | = 5 – 3
| x | = 2
`=>` x ∈ { ±2 }
Vậy x ∈ { ±2 }
c, `3^(x+1)` . 15 + `3^(x+1)` . 12 = `3^21`
`3^(x+1)` . ( 15 + 12 ) = `3^21`
`3^(x+1)` . 27 = `3^21`
`3^(x+1)` . `3^3` = `3^21`
`3^(x+1)` = `3^21` : `3^3`
`3^(x+1)` = `3^18`
`=>` x + 1 = 18
`=>` x = 18 + 1
`=>` x = 19
Vậy x = 19