Bài 1 : tìm số nguyên x, biết :
a, x + { ( x + 3 ) – [ ( x + 3 ) – ( – x – 2 )]} = x
Bài 2 : rút gọn các biểu thức :
a, x + 45 – [ 90 + ( – 20 ) + 5 – ( – 45 )]
b, x + ( 294 + 13 ) + ( 94 – 13 )
bài 3 : bỏ ngoặc rồi thu gọn các biểu thức sau :
a, (a + b) – (a – b) + (a – c) – (a + c)
b, (a + b – c) + (a – b + c) – (b + c – a) – (a – b – c)
Bài 1 : tìm số nguyên x, biết :
x + { ( x + 3 ) – [ ( x + 3 ) – ( – x – 2 )]} = x
<=> x + (x+3) – [ (x+3) – (-x-2) ] = x
<=> x + (x+3) – (x+3) + (-x-2) = x
<=> x + x + 3 – x – 3 -x – 2 = x
<=> -2 = x
<=> x = -2
Bài 2 : Rút gọn các biểu thức :
a, x + 45 – [ 90 + ( – 20 ) + 5 – ( – 45 )]
= x + 45 – 90 + 20 – 5 – 45
= x – 75
b, x + ( 294 + 13 ) + ( 94 – 13 )
= x + 294 + 13 + 94 – 13
= x + 388
Bài 3: Bỏ ngoặc rồi thu gọn các biểu thức sau :
a, (a + b) – (a – b) + (a – c) – (a + c)
= a + b – a + b + a – c – a – c
= a – a + a – a + b + b – c – c
= 2b – 2c
= 2 (b – c)
b, (a + b – c) + (a – b + c) – (b + c – a) – (a – b – c)
= a + b – c + a – b + c – b – c + a – a + b + c
= a + a + a – a + b – b – b + b – c + c – c + c
= 2a
Bài `1`
`x + { ( x + 3 ) – [ ( x + 3 ) – ( – x – 2 )]} = x `
`<=> x + (x+3) – [ (x+3) – (-x-2) ] = x`
`<=> x + (x+3) – (x+3) + (-x-2) = x`
`<=> x + x + 3 – x – 3 -x – 2 = x`
`<=> -2 = x `
`<=> x = -2`
`—————`
Bài `2`
`a) x + 45 – [ 90 + ( – 20 ) + 5 – ( – 45 )]`
`= x + 45 – 90 + 20 – 5 – 45`
`= x – 75`
`b) x + ( 294 + 13 ) + ( 94 – 13 )`
`= x + 294 + 13 + 94 – 13`
`= x + 388`
`—————`
Bài `3`
`a) (a + b) – (a – b) + (a – c) – (a + c)`
`= a + b – a + b + a – c – a – c`
`= a – a + a – a + b + b – c – c`
`= 2b – 2c`
`= 2 (b – c)`
`b) (a + b – c) + (a – b + c) – (b + c – a) – (a – b – c) `
`= a + b – c + a – b + c – b – c + a – a + b + c`
`= a + a + a – a + b – b – b + b – c + c – c + c`
`= 2a`