Toán Lớp 7: 1> (3x-1) ( 2x+7) –(x+1) (6x-5)
2> (3x-5) (7-5x) + (5x+2) (3x-2)-2
3> x(x-1/3) -1/2x (2x-3)
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Toán Lớp 7: 1> (3x-1) ( 2x+7) –(x+1) (6x-5)
2> (3x-5) (7-5x) + (5x+2) (3x-2)-2
3> x(x-1/3) -1/2x (2x-3)
Comments ( 2 )
1)\\
\left( {3x – 1} \right)\left( {2x + 7} \right) – \left( {x + 1} \right)\left( {6x – 5} \right)\\
= 6{x^2} + 21x – 2x – 7 – \left( {6{x^2} – 5x + 6x – 5} \right)\\
= 6{x^2} + 19x – 7 – 6{x^2} – x + 5\\
= 18x – 2\\
2)\\
\left( {3x – 5} \right)\left( {7 – 5x} \right) + \left( {5x + 2} \right)\left( {3x – 2} \right) – 2\\
= 21x – 15{x^2} – 35 + 25x\\
+ 15{x^2} – 10x + 6x – 4 – 2\\
= 42x – 41\\
3)x\left( {x – \dfrac{1}{3}} \right) – \dfrac{1}{2}x\left( {2x – 3} \right)\\
= {x^2} – \dfrac{1}{3}x – {x^2} + \dfrac{3}{2}x\\
= \dfrac{3}{2}x – \dfrac{1}{3}x\\
= \dfrac{7}{6}x
\end{array}$