3.( 2.X + 4 ) + 2.( 3.X -3 ) = 4.X + 94
5.( 2.X -1 ) - 3.( 2.X - 2 ) = 2.X +29
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A = 1x2 + 2x3 + 3x4 + ……….. + 29 x30
A x 3 = 1x2x3 + 2x3x3 + 3x4x3 + ……… + 29x30x3 Ax3 = 1x2x3 + 2x3x(4-1) + 3x4x(5-2) +………… 29x30x(31-28)
Ax3 = 1x2x3 + 2x3x4 -1x2x3 + 3x4x5 – 2x3x4 +……..+ 29x30x31 – 28x29x30 Ax3 = 29x30x31
A = 29x30x31 : 3
A = 290x31
A = 1x2 + 2x3 + 3x4 + ……….. + 29 x30
A x 3 = 1x2x3 + 2x3x3 + 3x4x3 + ……… + 29x30x3
Ax3 = 1x2x3 + 2x3x(4-1) + 3x4x(5-2) +………… 29x30x(31-28)
Ax3 = 1x2x3 + 2x3x4 -1x2x3 + 3x4x5 – 2x3x4 +……..+ 29x30x31 – 28x29x30
Ax3 = 29x30x31
A = 29x30x31 : 3
A = 290x31
Cho \(A=1\cdot2+2\cdot3+...+28\cdot29+29\cdot30\)
\(3A=1\cdot2\cdot3-1\cdot2\cdot3+2\cdot3\cdot4-2\cdot3\cdot4+...+29\cdot30\cdot31\)
\(3A=29\cdot30\cdot31\)
\(A=\left(29\cdot30\cdot31\right):3=29\cdot10\cdot31=8990\)
a) \(3.\left(2x+4\right)+2.\left(3x-3\right)=4x+94\)
\(\Rightarrow6x+12+6x-6=4x+94\)
\(\Rightarrow\left(6x+6x\right)+\left(12-6\right)=4x+94\)
\(\Rightarrow12x+6=4x+94\)
\(\Rightarrow12x-4x=94-6\)
\(\Rightarrow8x=88\Leftrightarrow x=11\)
b) \(5.\left(2x-1\right)-3.\left(2x-2\right)=2x+29\)
\(\Rightarrow10x-5-6x-6=2x+29\)
\(\Rightarrow\left(10x-6x\right)+\left(-5-6\right)=2x+29\)
\(\Rightarrow4x-11=2x+29\)
\(\Rightarrow4x-2x=29+11\)
\(\Rightarrow2x=30\Leftrightarrow x=15\)
mk làm lun
1,= 6x+12+5x-6= 4x+94
= 12x +6 = 4x+94
= 8x= 88
x= 11
2,= 10x-5-6x+6= 2x+29
= 4x+1= 2x+29
= 2x= 28
x= 14