Toán Lớp 8: Rút gọn các biểu thức sau
a, 2(3x-1)+5x (x-1)
b, (x-2) (x+2)-(x-1) (x+1)
c, (x-3)²-2(x-3)(x+7)+(x+7) ²
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Toán Lớp 8: Rút gọn các biểu thức sau
a, 2(3x-1)+5x (x-1)
b, (x-2) (x+2)-(x-1) (x+1)
c, (x-3)²-2(x-3)(x+7)+(x+7) ²
Comments ( 2 )
a,{\rm{ }}2\left( {3x – 1} \right) + 5x{\rm{ }}\left( {x – 1} \right)\\
= 6x – 2 + 5{x^2} – 5x\\
= x – 2 + 5{x^2}\\
b,{\rm{ }}\left( {x – 2} \right){\rm{ }}\left( {x + 2} \right) – \left( {x – 1} \right){\rm{ }}\left( {x + 1} \right)\\
= \left( {{x^2} – 4} \right) – \left( {{x^2} – {1^2}} \right)\\
= {x^2} – 4 – {x^2} + 1\\
= – 3\\
c,{\rm{ }}\left( {x – 3} \right) – 2\left( {x – 3} \right)\left( {x + 7} \right) + \left( {x + 7} \right){\rm{ }}\\
= {\left[ {\left( {x – 3} \right) – \left( {x + 7} \right)} \right]^2}\\
= {\left( {x – 3 – x – 7} \right)^2}\\
= 100
\end{array}\]