Tìm A biết \(\frac{4x^2-16}{x^2+2x}\)=\(\frac{A}{x}\)
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\(\frac{4x^2-16}{x^2+2x}=\frac{A}{x}\)\(\Leftrightarrow\frac{4\left(x^2-4\right)}{x\left(x+2\right)}=\frac{A}{x}\)
\(\Leftrightarrow\frac{4\left(x+2\right)\left(x-2\right)}{x\left(x+2\right)}=\frac{A}{x}\)\(\Leftrightarrow\frac{4\left(x-2\right)}{x}=\frac{A}{x}\)
\(\Leftrightarrow4\left(x-2\right)=A\Leftrightarrow A=4x-8\)
\(\frac{x}{x^2-2x}=\frac{B}{4x^2-16}\Leftrightarrow\frac{x}{x\left(x-2\right)}=\frac{B}{\left(2x+4\right)\left(2x-4\right)}\)
\(\Leftrightarrow x\left(2x+4\right)\left(2x-4\right)=x\left(x-2\right).B\)
\(\Rightarrow B=\frac{x.\left[2\left(x+2\right)\right].\left[2\left(x-2\right)\right]}{x\left(x-2\right)}=\frac{x.2\left(x+2\right).2\left(x-2\right)}{x\left(x-2\right)}\)
\(B=\frac{x.4\left(x+2\right)\left(x-2\right)}{x\left(x-2\right)}=4\left(x+2\right)\)
\(\frac{x}{x^2-2x}=\frac{B}{4x^2-16}\)
\(\frac{x}{x\left(x-2\right)}=\frac{B}{4.\left(x^2-4\right)}\)
\(\frac{1}{x-2}=\frac{B}{4.\left(x^2-4\right)}\)
\(\Rightarrow B.\left(x-2\right)=4.\left(x-2\right)\left(x+2\right)\)
\(B=4.\left(x+2\right)\)
\(B=4x+8\)
Làm đc 2 bài đầu chưa, t làm câu cuối cho, hai câu đầu dễ í mà
\(\frac{4x^2-16}{x^2+2x}=\frac{A}{x}\)
\(\Rightarrow A.\left(x^2+2x\right)=\left(4x^2-16\right).x\)
\(\Rightarrow A=\frac{\left[\left(2x\right)^2-4^2\right].x}{x^2+2x}\)
\(A=\frac{\left(2x-4\right)\left(2x+4\right).x}{x\left(x+2\right)}\)
\(A=\frac{2.2.\left(x-2\right)\left(x+2\right).x}{x\left(x+2\right)}\)
\(A=4\left(x-2\right)\)\(\left(x\ne0;x+2\ne0\right)\)
\(A=4x-8\)