1/4 : x = -11/2

x= 1/4 . 2/11

x= 1/-22

HT

x² - y² + 2y - 22 = 0

<=> x² - y² + y + y - 1 = 21

<=> x² - y(y - 1) + (y - 1) = 21

<=> x² - (y + 1)(y - 1) = 21

<=> x² - (y - 1)² = 21

=> x² - x(y - 1) + x(y - 1) - (y - 1)² = 21

<=> x(x - y + 1) + (y - 1)(x - y + 1) = 21

<=> (x + y - 1)(x - y + 1) = 21

Lập bảng xét các trường hợp 

\(\frac{-4}{7}-x=\frac{3}{5}-2x\)

\(\Rightarrow\frac{-4}{7}-x+2x=\frac{3}{5}\)

\(\Rightarrow\frac{-4}{7}+x=\frac{3}{5}\)

\(\Rightarrow x=\frac{3}{5}-\left(-\frac{4}{7}\right)\)

\(\Rightarrow x=\frac{41}{35}\)

Đề như này vẫn đúng nhé?

\(\frac{1}{98}-\frac{1}{98.97}-...-\frac{1}{3.2}-\frac{1}{2.1}\)

\(=\frac{1}{98}-\left(\frac{1}{98.97}+...+\frac{1}{3.2}+\frac{1}{2.1}\right)\)

\(=\frac{1}{98}-\left(\frac{1}{1.2}+\frac{1}{2.3}+...+\frac{1}{97.98}\right)\)

\(=\frac{1}{98}-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{97}-\frac{1}{98}\right)\)

\(=\frac{1}{98}-\left(1-\frac{1}{98}\right)\)

\(=\left(\frac{1}{98}+\frac{1}{98}\right)-1\)

\(=\frac{-48}{49}\)

sao chỗ kia lại nhân với 1

?????/

Ta có :

\(A=\frac{1}{3}-\frac{3}{4}-\left(-\frac{3}{5}\right)+\frac{1}{72}-\frac{2}{9}-\frac{1}{36}+\frac{1}{15}\)

\(\Rightarrow A=\frac{5}{15}-\frac{54}{72}+\frac{9}{15}+\frac{1}{72}-\frac{16}{72}-\frac{1}{72}+\frac{1}{15}\)

\(\Rightarrow A=\left(\frac{5}{15}+\frac{9}{15}+\frac{1}{15}\right)+\left(-\frac{54}{72}+\frac{1}{72}-\frac{16}{72}-\frac{2}{72}\right)\)

\(\Rightarrow A=1-\frac{71}{72}=\frac{1}{72}\)