Toán Lớp 8: Đề bài: Rút gọn biểu thức:
a) A= (x+2) x^2- 2x+4- x^3+2
b) B= (x-1) x^2+x+1-(x-1) x^2-1+1
c) C= (2x-y) 4x^2+2xy+y^2+(y-3x) y^2 +3xy+9x^2
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Toán Lớp 8: Đề bài: Rút gọn biểu thức:
a) A= (x+2) x^2- 2x+4- x^3+2
b) B= (x-1) x^2+x+1-(x-1) x^2-1+1
c) C= (2x-y) 4x^2+2xy+y^2+(y-3x) y^2 +3xy+9x^2
Comments ( 1 )
a)A = \left( {x + 2} \right){x^2} – 2x + 4 – {x^3} + 2\\
= {x^3} + 2{x^2} – 2x + 4 – {x^3} + 2\\
= 2{x^2} – 2x + 6\\
b)B = \left( {x – 1} \right)\left( {{x^2} + x + 1} \right) – \left( {x – 1} \right)\left( {{x^2} – 1} \right) + 1\\
= {x^3} – 1 – \left( {{x^3} – x – {x^2} + 1} \right) + 1\\
= {x^2} + x – 1\\
c)C = \left( {2x – y} \right)\left( {4{x^2} + 2xy + {y^2}} \right) + \left( {y – 3x} \right).\left( {{y^2} + 3xy + 9{x^2}} \right)\\
= {\left( {2x} \right)^3} – {y^3} + {y^3} – {\left( {3x} \right)^3}\\
= 8{x^3} – 27{x^3}\\
= – 19{x^3}
\end{array}$