haizz

nhìn vội quá ko để ý dấu trừ

\(\dfrac{2}{15}-\dfrac{7}{10}=\dfrac{4}{30}-\dfrac{21}{30}=-\dfrac{17}{30}\)

\(\dfrac{7}{4}-\dfrac{2}{3}=\dfrac{21}{12}-\dfrac{8}{12}=\dfrac{13}{12}\)

a)\(\left(x+2y\right)^2=x^2+4xy+4y^2\)

b)\(\left(5x-y\right)^2=25x^2-10xy+y^2\)

c)\(\left(x^2+\dfrac{2}{5}y\right).\left(x^2-\dfrac{2}{5}y\right)=x^4-\dfrac{4}{25}y^2\)

d)\(\left(3x^2-2y\right)^3=27x^6-54x^4y+36x^2y^2-8y^3\)

e)\(\left(x+2y+z\right).\left(x+2y-z\right)=\left(x+2y\right)^2+z^2\)

f)\(\left(x^2-3\right).\left(x^{\text{4}}+3x^2+9\right)=x^6-27\)