Toán Lớp 8: Phân tích đưa thức thành ngân tử:
-3x^2+7x-4
Làm 3 cách
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Toán Lớp 8: Phân tích đưa thức thành ngân tử:
-3x^2+7x-4
Làm 3 cách
Comments ( 2 )
C1) – 3{x^2} + 7x – 4\\
= – 3{x^2} + 3x + 4x – 4\\
= – 3x\left( {x – 1} \right) + 4\left( {x – 1} \right)\\
= \left( {x – 1} \right)\left( { – 3x + 4} \right)\\
= \left( {x – 1} \right)\left( {4 – 3x} \right)\\
C2)\\
– 3{x^2} + 7x – 4\\
= – 3{x^2} + 4x + 3x – 4\\
= – x\left( {3x – 4} \right) + \left( {3x – 4} \right)\\
= \left( {3x – 4} \right)\left( { – x + 1} \right)\\
= \left( {3x – 4} \right).\left( {1 – x} \right)\\
C3)\\
– 3{x^2} + 7x – 4\\
= – 3.\left( {{x^2} – \dfrac{7}{3}x + \dfrac{4}{3}} \right)\\
= – 3.\left( {{x^2} – 2.x.\dfrac{7}{6} + \dfrac{{49}}{{36}} – \dfrac{1}{{36}}} \right)\\
= – 3.\left[ {{{\left( {x – \dfrac{7}{6}} \right)}^2} – \dfrac{1}{{36}}} \right]\\
= – 3.\left( {x – \dfrac{7}{6} – \dfrac{1}{6}} \right)\left( {x – \dfrac{7}{6} + \dfrac{1}{6}} \right)\\
= – 3.\left( {x – \dfrac{4}{3}} \right).\left( {x – 1} \right)\\
= \left( {4 – 3x} \right)\left( {x – 1} \right)
\end{array}$