Toán Lớp 7: Rút gọn rồi tính giá trị biểu thức.
a.A= 3.(x-1)-3x.(5+x)-2/3.Với x=-1/3
b.B=3.(1-2x)-2.(2x-1)-2/5.Với x=-1/5
c.C=-(x-4)+2.(3-x)-5x.Với x=-1
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Toán Lớp 7: Rút gọn rồi tính giá trị biểu thức.
a.A= 3.(x-1)-3x.(5+x)-2/3.Với x=-1/3
b.B=3.(1-2x)-2.(2x-1)-2/5.Với x=-1/5
c.C=-(x-4)+2.(3-x)-5x.Với x=-1
Comments ( 1 )
a)A = 3\left( {x – 1} \right) – 3x\left( {5 + x} \right) – \dfrac{2}{3}\\
= 3x – 3 – 15x – 3{x^2} – \dfrac{2}{3}\\
= – 3{x^2} – 12x – \dfrac{{11}}{3}\\
= – 3.{\left( {\dfrac{{ – 1}}{3}} \right)^2} – 12.\left( {\dfrac{{ – 1}}{3}} \right) – \dfrac{{11}}{3}\\
= \dfrac{{ – 1}}{3} + 4 – \dfrac{{11}}{3}\\
= 0\\
b)B = 3.\left( {1 – 2x} \right) – 2\left( {2x – 1} \right) – \dfrac{2}{5}\\
= 3 – 6x – 4x + 2 – \dfrac{2}{5}\\
= 5 – \dfrac{2}{5} – 10x\\
= \dfrac{{23}}{5} – 10x\\
= \dfrac{{23}}{5} – 10.\dfrac{{ – 1}}{5}\\
= \dfrac{{23}}{5} + 2\\
= \dfrac{{33}}{5}\\
c)C = – \left( {x – 4} \right) + 2\left( {3 – x} \right) – 5x\\
= – x + 4 + 6 – 2x – 5x\\
= 10 – 8x\\
= 10 – 8.\left( { – 1} \right)\\
= 18
\end{array}$