\[\begin{array}{l}
\underline {\# andy} \\
1)\\
a)3x.\left( {4{x^3} - 6x + 5} \right)\\
 = \left( {3x.4{x^3}} \right) - \left( {3x.6x} \right) + \left( {3x.5} \right)\\
 = 12{x^4} + 18x + 15x\\
b)4{x^3}.\left( {3{x^2} + 5x - \dfrac{1}{2}} \right)\\
 = \left( {4{x^3}.3{x^2}} \right) + \left( {4{x^3}.5x} \right) - \left( {4{x^3}.\dfrac{1}{2}} \right)\\
 = 12{x^5} + 20{x^4} - 2{x^3}\\
\\
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\\
\\
2)\\
a)\left( {x + 3} \right)\left( {x + 6} \right)\\
 = \left( {x.x} \right) + \left( {x.6} \right) + \left( {3.x} \right) + \left( {3.6} \right)\\
 = {x^2} + 6x + 3x + 18\\
 = {x^2} + 9x + 18\\
b)\left( {x + 2} \right)\left( {x + 7} \right)\\
 = \left( {x.x} \right) + \left( {x.7} \right) + \left( {2.x} \right) + \left( {2.7} \right)\\
 = {x^2} + 7x + 2x + 14\\
 = {x^2} + 9x + 14\\
c)\left( {x + 5} \right)\left( {x + 8} \right)\\
 = \left( {x.x} \right) + \left( {8.x} \right) + \left( {5.x} \right) + \left( {5.8} \right)\\
 = {x^2} + 8x + 5x + 40\\
{x^2} + 13x + 40
\end{array}\]

`#Studywell`

Thực hiện phép tính

`a, 3x . ( 4x^3 - 6x + 5 )`

`= 3x . 4x^3 - 3x . 6x + 3x . 5`

`= 12x^4 - 18x +  15`

`b, 4x^3 . ( 3x^2 + 5x - 1/2 )`

`= 4x^3 . 3x^2 + 4x^3 . 5x - 4x^3 . 1/2`

`= 12x^5 + 20x^4 - 2x^3`

Thực hiện phép tính

`a, ( x + 3 ) ( x + 6 ) = x^2 + 6x + 3x + 18 = x^2 + 9x + 18`

`b, ( x + 2 ) ( x + 7 ) = x^2 + 7x + 2x + 14 = x^2 + 9x + 14`

`c, ( x + 5 ) ( x + 8 ) = x^2 + 8x + 5x + 30 = x^2 + 13x + 30`