Câu 1: Toán đa thức, phân thức a/ ( 5x + 3 )( 2 – x ) b/ ( x – 1 ) ^2 + 4x ^2 – 5x c/ ( x – 3 )( x + 3 ) d/ ( x + 3)(x – 3 ) – x ^2 e/ ( x – 2 )( x

Đáp án:

$\begin{array}{l}
a)\left( {5x + 3} \right)\left( {2 – x} \right)\\
 = 10x – 5{x^2} + 6 – 3x\\
 =  – 5{x^2} + 7x + 6\\
b){\left( {x – 1} \right)^2} + 4{x^2} – 5x\\
 = {x^2} – 2x + 1 + 4{x^2} – 5x\\
 = 5{x^2} – 7x + 1\\
c)\left( {x – 3} \right)\left( {x + 3} \right)\\
 = {x^2} – 9\\
d)\left( {x + 3} \right)\left( {x – 3} \right) – {x^2}\\
 = {x^2} – 9 – {x^2}\\
 =  – 9\\
e)\left( {x – 2} \right)\left( {x + 5} \right) + x\left( {2 – x} \right)\\
 = \left( {x – 2} \right)\left( {x + 5} \right) – x\left( {x – 2} \right)\\
 = \left( {x – 2} \right)\left( {x + 5 – x} \right)\\
 = \left( {x – 2} \right).5\\
 = 5x – 10\\
f){\left( {x – 3} \right)^2} + x\left( {6 – x} \right)\\
 = {x^2} – 6x + 9 + 6x – {x^2}\\
 = 9
\end{array}$