a: S

b: Đ

a) S

b) Đ

\(a,\dfrac{6\times2+4}{7\times2}=\dfrac{12+4}{14}=\dfrac{16}{14}=\dfrac{8}{7}\\ \Rightarrow S\\ b,\dfrac{6\times2+4}{7\times2+4}=\dfrac{16}{18}=\dfrac{8}{9}\\ \RightarrowĐ\)

a) P(x) = 7x² . (x² – 5x + 2 ) – 5x .(x³ – 7x² + 3x)

= 7x² . x² + 7x² . (-5x) + 7x² . 2 – [5x. x³ + 5x . (-7x²) + 5x . 3x]

= 7. (x² . x²) + [7.(-5)] . (x² . x) + (7.2).x²  – {5. (x.x³) + [5.(-7)]. (x.x²) + (5.3).(x.x)}

= 7x⁴ + (-35). x³ + 14x²  – [ 5x⁴ + (-35)x³ + 15x² ]

= 7x⁴ + (-35). x³ + 14x²   - 5x⁴ + 35x³ - 15x²

= (7x⁴ – 5x⁴) + [(-35). x³ + 35x³ ] + (14x² - 15x² )

= 2x⁴ + 0 - x² 

= 2x⁴ – x²

b) Thay x = \( - \dfrac{1}{2}\) vào P(x), ta được:

P(\( - \dfrac{1}{2}\)) = 2. (\( - \dfrac{1}{2}\))⁴ –  (\( - \dfrac{1}{2}\))² \))

 \(\begin{array}{l} = 2.\dfrac{1}{{16}} - \dfrac{1}{4} \\ = \dfrac{1}{8} - \dfrac{{2}}{8} \\ = \dfrac{-1}{8} \end{array}\)

7+7×2

=7+14

=21

=7.3=21

7 + 7 x 2

= 7 + 14

= 21

9x9+7x2=81+14=95

kich đúng cho tớ nhé

81+14=95

9 x 9 + 7 x 2 = 81 + 14 

                   = 95

2x³-7x²+5x=0

<=>x*(2x²-7x+5)=0

<=>x*(2x²-2x-5x+5)=0

<=>x*[(2x²-2x)-(5x-5)]=0

<=>x*[2x*(x-1)-5*(x-1)]=0

<=>x*(x-1)*(2x-5)=0

\(a=1;b=-7;c=6\)

Vì \(a+b+c=1-7+6=0\)

Nên \(x_1=1;x_2=\dfrac{c}{a}=\dfrac{6}{1}=6\)

Vậy \(S=\left\{1;6\right\}\)