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Câu 1 :
a, \(\frac{3}{x+3}-\frac{x-6}{x^2+3x}=\frac{3x-x+6}{x\left(x+3\right)}=\frac{2x+6}{x\left(x+3\right)}=\frac{2}{x}\)
b, \(\frac{2x^2-x}{x-1}+\frac{x+1}{1-x}+\frac{2-x^2}{x-1}=\frac{2x^2-x-x-1+2-x^2}{x-1}\)
\(=\frac{x^2-2x+1}{x-1}=\frac{\left(x-1\right)^2}{x-1}=x-1\)
Bài 2 :
a, Với \(x\ne\pm2\)
\(A=\left(\frac{x}{x^2-4}+\frac{1}{x+2}-\frac{2}{x-2}\right):\left(1-\frac{x}{x+2}\right)\)
\(=\left(\frac{x+x-2-2\left(x+2\right)}{\left(x-2\right)\left(x+2\right)}\right):\left(\frac{x+2-x}{x+2}\right)\)
\(=\frac{-6}{\left(x-2\right)\left(x+2\right)}.\frac{x+2}{2}=\frac{-3}{x-2}\)
b, Thay x = -4 vào biểu thức trên ta được :
\(-\frac{3}{-4-2}=-\frac{3}{-6}=\frac{1}{2}\)
c, Để A \(\inℤ\Rightarrow x-2\inƯ\left(-3\right)=\left\{\pm1;\pm3\right\}\)
| x - 2 | 1 | -1 | 3 | -3 |
| x | 3 | 1 | 5 | -1 |
\(\frac{1}{X-1}-\frac{X^3-X}{X^2+1}\left(\frac{1}{X^2-2X+1}+\frac{1}{1-X^2}\right)\)
=\(\frac{1}{X-1}-\frac{X^3-X}{X^2+1}.\frac{X+1+X-1}{\left(X-1\right)^2\left(X+1\right)}\)
=\(\frac{1}{X-1}-\frac{X\left(X^2-1\right)}{X^2+1}.\frac{2X}{\left(X-1\right)^2\left(X+1\right)}\)
bài 1.
a.\(\left(x+4\right)\left(x^2-4x+16\right)=x^3-4^3=x^3-64\)
b.\(\left(x^2-\frac{1}{3}\right)\left(x^4+\frac{1}{3}x^2+\frac{1}{9}\right)=\left(x^2\right)^3-\left(\frac{1}{3}\right)^3=x^6-\frac{1}{27}\)
bài 2.
a.\(892^2+892.216+108^2=892^2+2.892.108+108^2\)
\(=\left(892+108\right)^2=1000^2=1_{ }000_{ }000\)
b.\(36^2+26^2-52.36=36^2+26^2-2.26.36=\left(36-26\right)^2=10^2=100\)
\(1.\left(\sqrt{x}+1\right)\left(\sqrt{x}-2\right)\)
\(=\sqrt{x}\left(\sqrt{x}-2\right)+1\left(\sqrt{x}-2\right)\)
\(=x-2\sqrt{x}+\sqrt{x}-2\)
\(=x-\sqrt{x}-2\)
\(2.\left(x+4\right)\left(x-2\right)-\left(x-3\right)^2\)
\(=x\left(x-2\right)+4\left(x-2\right)-\left(x^2-6x+9\right)\)
\(=x^2-2x+4x-8-x^2+6x-9\)
\(=8x-17\)
Chọn đáp án A