Toán Lớp 8: Rút gọn các biểu thức sau:
a) (x + 2) (x – 2) + 5 (x – 4)
b) (3x^3 – 2x^2 + 9x – 6) : (x^2 + 3)
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Toán Lớp 8: Rút gọn các biểu thức sau:
a) (x + 2) (x – 2) + 5 (x – 4)
b) (3x^3 – 2x^2 + 9x – 6) : (x^2 + 3)
Comments ( 1 )
a)\left( {x + 2} \right)\left( {x – 2} \right) + 5\left( {x – 4} \right)\\
= {x^2} – {2^2} + 5x – 20\\
= {x^2} – 4 + 5x – 20\\
= {x^2} + 5x – 24\\
b)\left( {3{x^3} – 2{x^2} + 9x – 6} \right):\left( {{x^2} + 3} \right)\\
= \left( {3{x^3} + 9x – 2{x^2} – 6} \right):\left( {{x^2} + 3} \right)\\
= \left( {\left( {{x^2} + 3} \right).3x – \left( {{x^2} + 3} \right).2} \right):\left( {{x^2} + 3} \right)\\
= \left( {{x^2} + 3} \right)\left( {3x – 2} \right):\left( {{x^2} + 3} \right)\\
= 3x – 2
\end{array}$