Cách của Tuấn Anh Phan Nguyễn đây.

\(=\dfrac{1}{2}-\left[\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+...+\dfrac{1}{512}+\dfrac{1}{1024}\right]\)

\(=\dfrac{1}{2}-\left[\left(\dfrac{1}{2}-\dfrac{1}{4}\right)+\left(\dfrac{1}{4}-\dfrac{1}{8}\right)+\left(\dfrac{1}{8}-\dfrac{1}{16}\right)+...+\left(\dfrac{1}{512}-\dfrac{1}{1024}\right)\right]\)\(=\dfrac{1}{2}-\left(\dfrac{1}{2}-\dfrac{1}{1024}\right)=\dfrac{1}{1024}.\)

45-41+16=17

tick nhé

Đề sai

Thằng chảnh Nguyễn Ngọc Sáng!!!

b) Đặt x² +x +1 =y

=y(y+1)-12

=y² +4y -3y -12

= y(y+4) - 3(y+4)

=(y+4)(y-3)

=(x²+x+5)(x²+x-2)

a) (x+y)² - (x+y) -12

=(x+y)²- 4(x+y) + 3(x+y)-12

=(x+y)(x+y-4) + 3 ( x+y -4)

=(x+y-4)(x+y+3)

a) 15 - 15 - x = 21

-x =21

x =-21

b) 39 + x -39 = 50

x =50