Question

[Thanh Thủy]

Khai triển theo hằng đẳng thức 

a. (1/x - 5 ) ( 1/x + 5 )

b ( x/3 - y/4 ) ( x/3 + y/4 )

d. ( x/y - 2/3 ) ( x/y + 2/3 )

e ( 2x - 2/3 ) ( 2/3 + 2x )

g . ( 2x + 3/5 ) ( 3/5 -2x )

h, ( 1/2 x - 4/3 ) ( 4/3 + 1/2x ) 

i. ( 2/3x^2 - Y/2 ) 9 2/3X^2 + Y/2 )

Answer 1

[Nguyễn Thị Thương Hoài]

a; (\(\dfrac{1}{x}\) - 5)(\(\dfrac{1}{x}\) + 5)

= (\(\dfrac{1}{x}\))^2 -  5²

=  \(\dfrac{1}{x^2}\) - 25

b; (\(\dfrac{x}{3}\) - \(\dfrac{y}{4}\))(\(\dfrac{x}{3}\) + \(\dfrac{y}{4}\))

 = \(\left(\dfrac{x}{3}\right)^2\) - \(\left(\dfrac{y}{4}\right)^2\)

  =  \(\dfrac{x^2}{9}\) - \(\dfrac{y^2}{16}\)

Answer 2

[Nguyễn Thị Thương Hoài]

d; (\(\dfrac{x}{y}\) - \(\dfrac{2}{3}\) (\(\dfrac{x}{y}\)+\(\dfrac{2}{3}\))

= (\(\dfrac{x}{y}\))² - (\(\dfrac{2}{3}\))²

= \(\dfrac{x^2}{y^2}\) - \(\dfrac{4}{9}\)

e; (2\(x\) - \(\dfrac{2}{3}\))(\(\dfrac{2}{3}\) + 2\(x\))

= (2\(x\))² - (\(\dfrac{2}{3}\))²

= 4\(x^2\) - \(\dfrac{4}{9}\)