Toán Lớp 8: bài 1 tính
a, -2x(x+1)
b, 3x(x+1)-(x-y)(x-1)
c, (x+1)(y-1)+(y^2-1)(x-1)
d, -2x(x+y)-3y(y-1)
e, X^3-1.3x+(x-1)(x+2)
f, (-7x-1)(x-1)+3x(x^2-1)
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Toán Lớp 8: bài 1 tính
a, -2x(x+1)
b, 3x(x+1)-(x-y)(x-1)
c, (x+1)(y-1)+(y^2-1)(x-1)
d, -2x(x+y)-3y(y-1)
e, X^3-1.3x+(x-1)(x+2)
f, (-7x-1)(x-1)+3x(x^2-1)
Comments ( 1 )
a) – 2x\left( {x + 1} \right)\\
= – 2{x^2} – 2x\\
b)3x\left( {x + 1} \right) – \left( {x – y} \right)\left( {x – 1} \right)\\
= 3{x^2} + 3x – {x^2} + x + xy – y\\
= 2{x^2} + 4x + xy – y\\
c)\left( {x + 1} \right)\left( {y – 1} \right) + \left( {{y^2} – 1} \right)\left( {x – 1} \right)\\
= xy – x + y – 1 + x{y^2} – {y^2} – x + 1\\
= x{y^2} + xy – 2x + y – {y^2}\\
d) – 2x\left( {x + y} \right) – 3y\left( {y – 1} \right)\\
= – 2{x^2} – 2xy – 3{y^2} + 3y\\
e){x^3} – 1.3x + \left( {x – 1} \right)\left( {x + 2} \right)\\
= {x^3} – 3x + {x^2} + 2x – x – 2\\
= {x^3} + {x^2} – 2x – 2\\
f)\left( { – 7x – 1} \right)\left( {x – 1} \right) + 3x\left( {{x^2} – 1} \right)\\
= – 7{x^2} + 7x – x + 1 + 3{x^3} – 3x\\
= 3{x^3} – 7{x^2} + 3x + 1
\end{array}$