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20 tháng 11 2015

Nhớ ghi dấu ngoặc tránh giải sai. 

\(a.\)  \(\frac{x+4}{2x+6}+\frac{3}{x^2-9}\)

Ta có: 

\(2x+6=2\left(x+3\right)\)

\(x^2-9=\left(x-3\right)\left(x+3\right)\)

nên \(MTC:\)  \(2\left(x-3\right)\left(x+3\right)\)

Do đó:  \(\frac{x+4}{2x+6}+\frac{3}{x^2-9}=\frac{x+4}{2\left(x+3\right)}+\frac{3}{\left(x-3\right)\left(x+3\right)}=\frac{\left(x+4\right)\left(x-3\right)}{2\left(x-3\right)\left(x+3\right)}+\frac{2.3}{2\left(x-3\right)\left(x+3\right)}=\frac{x^2+x-12+6}{2\left(x-3\right)\left(x+3\right)}\)

\(=\frac{x^2+x-6}{2\left(x-3\right)\left(x+3\right)}=\frac{x^2-2x+3x-6}{2\left(x-3\right)\left(x+3\right)}=\frac{x\left(x-2\right)+3\left(x-2\right)}{2\left(x-3\right)\left(x+3\right)}=\frac{\left(x-2\right)\left(x+3\right)}{2\left(x-3\right)\left(x+3\right)}=\frac{x-2}{2\left(x-3\right)}\)

 

20 tháng 11 2015

tick mình đi mình giải cho nha

20 tháng 11 2015

\(\frac{x+2}{x+1}=\frac{x}{x+1}+\frac{2}{x+1}\)

\(\frac{2x-3}{x-1}=\frac{2x}{x-1}+\frac{-3}{x-1}\)

\(\frac{x^2-3x+5}{x+1}=\frac{x^2}{x+1}+\frac{-3x+5}{x+1}\)

1 tháng 4 2020

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18 tháng 9 2020

tớ chịu.

hi hi.

1 tháng 11 2015

\(x^3+8x^2+17x+10\)

\(=x^3+2x^2+x^2+5x^2+10x+5x+2x+10\)

\(=\left(x^3+x^2\right)+\left(2x^2+2x\right)+\left(5x^2+5x\right)+\left(10x+10\right)\)

\(=x^2\left(x+1\right)+2x\left(x+1\right)+5x\left(x+1\right)+10\left(x+1\right)\)

\(=\left(x+1\right)\left(x^2+2x+5x+10\right)\)

\(=\left(x+1\right)\left[x\left(x+2\right)+5\left(x+2\right)\right]\)

\(=\left(x+1\right)\left(x+2\right)\left(x+5\right)\)

1 tháng 12 2015

câu b nè

\(\frac{3x+1}{\left(x-1\right)^2}-\frac{1}{x+1}-\frac{x+3}{x^2-1}\)

=\(\frac{\left(3x+1\right)\left(x+1\right)}{\left(x-1\right)^2\left(x+1\right)}-\frac{\left(x-1\right)^2}{\left(x-1\right)^2\left(x+1\right)}-\frac{\left(x+3\right)\left(x-1\right)}{\left(x-1\right)^2\left(x+1\right)}\)

=\(\frac{\left(3x^2+x+3x+1\right)-\left(x^2-2x+1\right)-\left(x^2-x-3+3x\right)}{\left(x-1\right)^2\left(x+1\right)}\)

=\(\frac{3x^2+4x+1-x^2+2x-1-x^2-2x+3}{\left(x-1\right)^2\left(x+1\right)}=\frac{x^2+4x+3}{\left(x+1\right)\left(x-1^2\right)}\)

=\(\frac{\left(x+1\right)\left(x+3\right)}{\left(x+1\right)\left(x-1\right)^2}=\frac{x+3}{\left(x-1\right)^2}\)