a) (x² – x) . (2x² – x – 10)

= x² . (2x² – x – 10) – x. (2x² – x – 10)

= x² . 2x² + x² . (-x) + x² .(-10) – [ x. 2x² + x. (-x) + x. (-10)]

= 2x⁴ – x³ - 10x² – (2x³ – x² – 10x)

= 2x⁴ – x³ - 10x² – 2x³ + x² + 10x

= 2x⁴ + (– x³ – 2x³ ) + (-10x² + x² )+ 10x

= 2x⁴ – 3x³ - 9x² + 10x

b) (0,2x² – 3x) . 5(x² -7x + 3)

= (0,2x² . 5 – 3x . 5) . (x² -7x + 3)

= (x² – 15x). (x² -7x + 3)

= x² . (x² -7x + 3) – 15x. (x² -7x + 3)

= x² . x² + x² . (-7x) + x² . 3 – [ 15x³ + 15x.(-7x) + 15x.3]

= x⁴ – 7x³ + 3x² – (15x³ – 105x² + 45x)

= x⁴ – 7x³ + 3x² – 15x³ + 105x² – 45x

= x⁴ +(– 7x³ – 15x³ )+ (3x² + 105x²) – 45x

= x⁴ – 22x³ + 108x² – 45x

a: =1/2x^3*x^2-1/2x^3*6x-1/2x^3*10

=1/2x^5-3x^4-5x^3

b: =-3x^2*5x^3+3x^2*4x^2-3x^2*3x+3x^2*3x

=-15x^5+12x^4-9x^3+9x^2

c: \(=3x\cdot5x^2-3x\cdot2x-3x=15x^3-6x^2-3x\)

d: \(=\dfrac{1}{2}x^2y\cdot2x^3-\dfrac{1}{2}x^2y\cdot\dfrac{2}{5}xy^2-\dfrac{1}{2}x^2y=x^5y-\dfrac{1}{5}x^3y^3-\dfrac{1}{2}x^2y\)

a,     (\(\dfrac{9}{10}\) - \(\dfrac{15}{16}\)) \(\times\) ( \(\dfrac{5}{12}\) - \(\dfrac{11}{15}\) - \(\dfrac{7}{20}\))

=  (\(\dfrac{72}{80}\) - \(\dfrac{75}{80}\))  \(\times\) (\(\)\(\dfrac{25}{60}\) - \(\dfrac{44}{60}\)  - \(\dfrac{21}{60}\))

= - \(\dfrac{3}{80}\)  \(\times\) (- \(\dfrac{2}{3}\))

= \(\dfrac{1}{40}\) 

b, (-1)³ + (- \(\dfrac{2}{3}\))² : 2\(\dfrac{2}{3}\) + \(\dfrac{5}{6}\)

=  -1³ +   \(\dfrac{4}{9}\) : \(\dfrac{8}{3}\) + \(\dfrac{5}{6}\)

= -1 + \(\dfrac{4}{9}\) \(\times\) \(\dfrac{3}{8}\) + \(\dfrac{5}{6}\)

= -1 + \(\dfrac{1}{6}\) + \(\dfrac{5}{6}\)
= -1 + 1

= 0

a.-1,75-(-\(\dfrac{1}{9}\)-2\(\dfrac{1}{8}\))
-1,75-\(\dfrac{1}{9}+\dfrac{17}{8}\)
\(-\dfrac{7}{4}-\dfrac{1}{9}+\dfrac{17}{8}\)
\(\dfrac{-126}{72}-\dfrac{8}{72}+\dfrac{153}{72}\)
=\(\dfrac{19}{72}\)

b.\(\dfrac{-1}{12}-\left(2\dfrac{5}{8}-\dfrac{1}{3}\right)\)
\(\dfrac{-1}{12}-\left(\dfrac{21}{8}-\dfrac{1}{3}\right)\)
\(\dfrac{-1}{12}-\dfrac{21}{8}+\dfrac{1}{3}\)
\(\dfrac{-2}{24}-\dfrac{63}{24}+\dfrac{64}{24}\)
=\(\dfrac{-1}{24}\)

\(\frac{-10}{11}×\frac{8}{9}+\frac{7}{18}×\frac{10}{11}\)

\(=\frac{10}{11}×\frac{-16}{18}+\frac{7}{18}×\frac{10}{11}\)

\(=\left(\frac{-16}{18}+\frac{7}{18}\right)×\frac{10}{11}\)

\(=\frac{1}{2}×\frac{10}{11}=\frac{5}{11}\)

\(\text{Giải :}\)

\(\frac{-10}{11}×\frac{8}{9}+\frac{7}{18}×\frac{10}{11}\)

\(=\frac{10}{11}×\frac{-16}{18}+\frac{7}{18}×\frac{10}{11}\)

\(=\left(\frac{-16}{18}+\frac{7}{18}\right)×\frac{10}{11}\)

\(=\frac{1}{2}×\frac{10}{11}\)

\(=\frac{5}{11}\)

\(\text{#Hok tốt!}\)

a: =3x^3-15x^2+21x

b: =-x^3+6x^2+5x-4x^2-24x-20

=-x^3+2x^2-19x-20

c: =9x^2+15x-3x-5-7x^2-14

=2x^2+12x-19

d: =10x^2-4x+2/3