` Bài 1 :`
`a, 13 . 65 + 35 . 12`
` = 845 + 420`
`= 1265`
`b, 31 + 32 + 33+ .... + 39 -21 - 22 - .... - 29 `
`= ( 31 - 21 )+ ( 32 - 22 ) + ........ + (39 - 29 )`
`= 10 + 10 + 10 +...... + 10` ( 9 cặp )
`= 90 `
`c, 3 - 8 . 27 + 4 . 33 .6 + 40 . 2 . 12`
`= 3 - 2 . 2.2 . 27 + 2 . 2 . 11 . 3 . 2 . 3 + 2 .2 .2 .5 .2.2 .2`
`= 3 - 27+11.5`
`= 31`
` Bài 2 :`
a) \(3\left(2x-5\right)+125=134\)
\(\Leftrightarrow3\left(2x-5\right)=9\)
\(\Leftrightarrow2x-5=3\)
\(\Leftrightarrow2x=8\Leftrightarrow x=4\)
b) \(\left(2x+5\right)+\left(2x+3\right)+\left(2x+1\right)=27\)
\(\Leftrightarrow6x+9=27\)`
\(\Leftrightarrow6x=18\Leftrightarrow x=3\)
d) \(27\left(x-27\right)-27=0\)
\(\Leftrightarrow27\left(x-27\right)=27\)
`x- 27 = 27 : 27 `
`x = 1 - 27 `
`x = - 26 `
` Bài 3:`
Vì x. y = 0 => x hoặc y = 0
Nếu x = 0 thì:
0+2y = 43
=> y=21,5
Nếu y = 0 thì:
x + 2. 0 = 43
=> x= 43
